"... This is the work of God, that you believe in him whom he has sent" (John 6:29, ESV).
"... [He] greatly helped those who through grace had believed" (Acts 18:27, ESV).
Infidels, who deny the existence of God, don't have a leg to stand on, and cannot defend their faith with any evidence whatsoever: neither circumstantial; logical; scientific; philosophical; nor historical. However, Christianity is a historical faith and there is plenty of evidence for anyone willing to believe and obey the truth; unbelievers are defined as those who "reject the truth," according to Romans 2:8. Claiming Christians have blind faith is offensive and insulting to God, and demeaning to believers!
There is no universal belief, but there is universal truth (objective, transcendent, and eternal) that applies whether believed or not: Because someone denies the truth, doesn't mean it's not true. People often confuse belief and truth, saying that they don't believe the Bible, for instance, when you don't have to believe it to be saved; however, most who say they don't believe the Bible, don't know what its message is or have never read it! The Bible is a caged lion, in that it defends itself, and need not appeal to any higher authority than itself for attestation.
The proof for Christ and His resurrection is mostly circumstantial and historical, and any one piece of evidence isn't conclusive, but the totality of the evidence is most compelling and one must go in the direction of the preponderance of the evidence if one is reasonable or in a court of law. It has been stated by Dr. Simon Greenleaf, Royal Professor of Law at Harvard University (considered the world's foremost expert on law and evidence) that any unbiased jury would declare the biblical account a fact of history. (He wrote a book, though a skeptic at first, declaring his conversion after examining the evidence, The Testimony of the Evangelists.)
No event in history has been so widely and variously proved than this; in fact, Luke says, "there are many infallible proofs" in Acts 1:3. It is arguably the best attested fact in antiquity. God won't force anyone to believe against his will, but he must want to believe and then God will work on his heart and will to make a believer out of him. (Note that faith is given, not achieved! It's demonstrated, not possessed because we see it in action, we don't talk about it!)
Now Christians are accused of having blind faith, whereas they have sound reasons for what they believe and God never asks anyone to believe despite the evidence--you cannot believe and trust in something you are not intellectually convinced of. But atheists seldom know why they are atheists and certainly cannot defend their position (logicians know you cannot prove a universal negative). Not knowing why you believe is a kind of blind faith. The problem today is not a willingness to believe, but people not knowing what they believe, which is a sort of unbelief and blind faith.
We don't have faith in faith, for faith doesn't save, Christ does! We don't have faith for faith sake, but it is directed in a person, not a creed or ritual. Religion is knowing a creed or the rules, Christianity is knowing a person! The Bible says, "Taste and see that the LORD is good" (cf. Psalm 34:8)--God confirms our faith and the Christian experience is valid and verifiable. He invites scrutiny! Our basis of feeling and of forgiveness is not purely rational but based on historical evidence of the objective fact of the resurrection. We are not being fooled by some colossal propaganda program! Many of the first-century believers died for their faith, and the "blood of the martyrs was the seed of the church," according to church father Tertullian.
We haven't kissed our brains goodbye but have used them. Faith doesn't reject the mind, it respects the mind. We don't go against reason, but beyond it. We must all take the step of faith into the light, but once there, our eyes are opened and we become enlightened by the Holy Spirit. Note that apart from the Holy Spirit, no one would believe. "We must cater to anyone's intellectual integrity, but not pander to their arrogance," according to John Stott. The problem is not intellectual, but moral; people don't want to believe, because their will is hardened: John 7:17 says that anyone willing to do His will, will know of the doctrine.
"...' You foolish people! You find it so hard to believe all that the prophets wrote in the Scriptures" (Luke 24:25, NLT).
"...' O foolish ones, and slow of heart to believe all that the prophets have spoken!'" (Ibid., NKJV).
"Therefore my people go into exile for lack of knowledge..." (Isaiah 5:13, ESV).
"...and a people without understanding shall come to ruin" (Hosea 4:14, ESV).
"...There is no faithfulness or steadfast love, and no knowledge of God in the land" (Hos. 4:1, ESV).
"For I desire steadfast love and not sacrifice, the knowledge of God rather than burnt offerings" (Hosea 6:6, ESV).
"Let us know; let us press on to know the LORD..." (Hosea 6:3, ESV).
"I don't have enough faith to be an atheist."--Norman L. Geisler, noted biblical scholar
Note: Not knowing what you believe is a kind of unbelief or blind faith.
Christians have sound, rational reasons to have faith in Christ: circumstantial evidence that is most compelling and unexplainable otherwise; the convicting work of the Holy Spirit, especially through the Word of God (its inspiration, transmission, and canonicity); the objective, cumulative, historical evidence of the resurrection; plus the subjective experience ("Oh, taste and see that the LORD is good..." cf. Psalm 34:8, NKJV) and value of knowing Christ personally ("[N]ow that you have had a taste of the Lord's kindness" cf. 1 Peter 2:3, NLT).
Christianity is the only faith that is based on fact, not a fable, fiction, myth, old wives' tales, legend, or tall tale--if it's not a historical religion, it's nothing at all. "For we did not follow cleverly devised myths..." (cf. 2 Pet. 1:16). The historical evidence is further validated by the veracity of the witnesses, who were willing to go to their deaths for their faith. One usually tells the truth on one's deathbed. It's not a matter of whether you believe the resurrection was possible, but are the historical records reliable, credible, dependable, and accurate? If there's a God, then resurrection is possible by deduction.
The difference between them dying for their faith and other martyrs of different faiths is that they were in the position to know whether it was true. Any faith not based on evidence is blind faith--even an atheist who doesn't know why he's one or has no evidence has blind faith. It's not a battle or challenge between faith and reason but faith versus faith!. It depends on which set of presuppositions one begins with and is willing to accept as true--secularists bet the farm on science being the only reliable source of truth. Secularists are people of faith too! If you say that you only believe what can be proved by the scientific method or empiricism, you must first begin by proving the validity of that premise.
Epistemological humility comes in to play where one admits he doesn't have a monopoly on the truth or know everything and is therefore teachable. In the final analysis, no preacher nor scientist has cornered the market on truth and can speak ex-cathedra or pontificate. Socrates said that to begin learning you must admit your ignorance! Uncertainty is the prerequisite to learning and often its byproduct! Education is merely going from an unconscious to a conscious awareness of your ignorance. Everyone must admit that they could be wrong--no one is infallible.
Christians today are inclined to believe that their faith is indefensible in the open marketplace of ideas, and don't know how to defend their faith or even know what they believe and should defend. We must not let secularists win by default or by concession--we must stand our ground and declare our colors! What is negotiable and what isn't? We have sound reasons to believe; God doesn't expect us to believe despite the evidence. God will reveal the truth to anyone who is willing to do His will (cf. John 7:17) and has an open mind, willing spirit, and needy heart. God doesn't expect us to believe contrary to reason, but will manifest Himself to us if we search for Him--He is no man's debtor.
Faith is a gift and choice but we must exercise it. The problem is when we become lax in the faith or our faith is dead, we can do nothing (John 15:5 says, "For apart from Me you can do nothing"), that faith doesn't save; only a living and growing faith that produces fruit can save--no fruit, no faith, no salvation. Saving faith is not a leap in the dark, but a step into the light--God asks no one to commit intellectual suicide and believe for the sake of believing alone (faith doesn't save, nor faith in faith, but only faith in Christ as the object saves). Faith feeds on facts and experience, while Paul said in Romans 10:17, NKJV, concerning that precious faith: "So then faith comes by hearing, and by hearing [i.e., preaching] by the word of God." We must mature in the faith and have childlike, not childish faith; simple, but not simplistic!
Christians can have strong faith, but if they aren't able to defend it or have a reason for their faith, it's blind faith and may succumb to the devil's Anfectung or attack. It's not how much faith, but the object of the faith that's vital-you can be sincerely wrong, though sincerity is a requisite. We are always to be ready to have a reason for our hope (cf. 1 Peter 3:15). In the study of apologetics, one will realize that Christians haven't kissed their brains goodbye, and that faith is rational, though Christianity isn't rationalism. God had a rationale for sending His Son and the gospel is about realizing that work of grace is done on our behalf.
In sum, the heart of the matter is that it's a matter of the heart; there's never enough evidence to convince the hardened skeptic, but there's ample evidence for the willing People are "slow of heart to believe." Christians cannot argue someone into the kingdom! But they should be able to have an answer as to why they believe (cf. 2 Tim. 2:15). The problem is that some people catch their beliefs like one catches a cold: hanging around the right people and letting osmosis do its work. Also, you don't have to be able to defend your faith to have it! However, you cannot rationalize God or put Him in a test tube or under laboratory conditions, because the existence of God is not in the scientific domain-- it takes faith and faith is what pleases God; skeptics are rarely convinced by debate--a work of grace must woo their hearts toward God. "This is the work of God, that you believe in Him whom He has sent." (cf. John 6:29). Soli Deo Gloria!