Andrew, unfortunately it appears that we are going to have to have a conversation about the definition of faith because you are right – if we use your definition, faith would be irrational.
The Bible defines faith as “the assurance of things hoped for, the conviction of things not seen.” (Hebrews 11:1). Note that it says nothing about “blind” faith, that is, believing something without evidence. Frankly, a person would be a fool to believe something without any evidence. Rather, the Biblical definition talks about having confidence in things that we hope for. We hope in things only when we have evidence for those things.
Perhaps, I was wrong to have started off with the Biblical definition. The definition in Webster’s, however, supports the Biblical definition:
1. Confident belief in the truth, value, or trustworthiness of a person, idea, or thing.
2. Belief that does not rest on logical proof or material evidence.
3. Loyalty to a person or thing; allegiance: keeping faith with one's supporters.
4. often Faith Christianity The theological virtue defined as secure belief in God and a trusting acceptance of God's will.
5. The body of dogma of a religion: the Muslim faith.
6. A set of principles or beliefs.
So, as you can see, your definition of faith is the second definition. The first definition of faith is the same as the Biblical definition, namely it means to “trust” or a “confident belief.” It is unfair and dishonest to accuse Christians of being irrational. We definitely have reasons for why we believe in God. There is plenty of evidence of the existence of God, it is just that the atheist, for whatever reason, chooses to reject that evidence. Indeed, as a Christian, I would not ask you to put your faith in something that is irrational or without evidence.
By the way, if we used your definition of faith, then belief in atheism is irrational. In other words, there is no evidence of atheism. Atheism is a disbelief in the existence of God. You would have to prove the non-existence of God, and an atheist cannot do that. Therefore, using your definition of faith, it is atheism that is irrational, not theism.