One unfortunate thing about being human is that we generally have to pool our knowledge. All of us, without exception, have huge amounts of faith, because it is impossible to literally test all of our beliefs. Instead, we must rely on faith, maybe even blind faith, in order to hold those beliefs.
Take, for example, germ theory. I assume most readers would agree that "have you ever seen a germ?" would be a foolish argument to suggest that germs do not exist, or that I shouldn't wash my hands before I eat, or that I should be just fine drinking water from any murky pool, or that it's totally safe to shake hands with someone who just coughed into theirs. And yet, personally, I have never seen a germ. Germ theory, therefore, is something I accept on faith.
This isn't something I accept on blind faith, however. If there were enough people running around arguing against germ theory, I would be quite capable of defending it. Thankfully, in my culture, there aren't. But other cultures are a different story.
Even in the modern world, some communities are so impoverished, they still need to collect water from rivers, or polluted wells. When charities, such as Lifewater International, seek to improve this situation, one of the major challenges they face is education. These communities are quite happy for the charities to help them obtain water, even clean water, yet it is still a struggle to convince them that the water they've been drinking all their lives might contain tiny organisms that threaten their physical health. In other words, there really are some people in this world who are skeptical of, and even stubbornly resistant to germ theory.
What this tells us is that there are actually more times when a lack of faith is unreasonable, rather than actually having faith. It is not unreasonable for me to have faith in germ theory, it is unreasonable for a Westerner to reject it. One could say that it is reasonable for those impoverished communities to be skeptical, given that they don't have our education, and it's not like you can show every individual person (especially those who have been literally blinded by polluted water) a germ. Much less what those germs can do. But even if you want to argue that their skepticism is reasonable, it is still factually wrong.
God and germ theory are rather different. Whereas germ theory is a theory, God is certainly not. No one observed a set of facts and made God up in an attempt to explain them. Neither did anyone happen to stumble upon God and start studying Him with progressively more advanced technology. Rather, God revealed Himself to man. From Adam to Noah to Abraham, Isaac, and Jacob to Moses to the prophets, right the way up to the Apostles, God has been very active throughout history. The greatest of His historical activities was the Incarnation: In the beginning was the word, and the word was with God, and the word was God, and the word became flesh: Jesus of Nazareth.
God quite literally became man. He was born of a virgin woman, He suckled at His mother's breasts, He stumbled to His feet on our very planet, He breathed our air. The sun He created is not even worthy to shimmer in His direction, and yet, like us, He became comparatively insignificant. The God who has to humble Himself just to observe the universe humbled Himself so much as to live in it as one of us.
This wasn't a holiday. This wasn't a scientific expedition. This, ladies and gentlemen, was a rescue mission. See, we have all rebelled against our God. He gave us a set of commandments, and we break them. There is only one suitable remedy: Death. But God does not desire our destruction, and so He sent Jesus to live a sinless life, not rebelling against Him as we do. Nevertheless, Jesus died. He died in front of a crowd, indeed the very crowd that demanded He be put to death via crucifixion. But He didn't stay dead. On the third day, Jesus walked out of His tomb and stepped into the sunlight once again. And after that, He made several public appearances to the very crowd before whom He died.
Through His death and resurrection, Jesus made it entirely possible to be reconciled to God. Our sins, which had previously separated us from Him, died with Jesus. All who put their faith in Him can rise with Him.