When Jesus says, “blessed are those who have not seen and yet believed,” he is speaking of something very specific, not making a comment in general about the nature of faith. What he is telling Thomas, in a kind of prophecy is, blessed are those who are not eye-witnesses of my bodily resurrection, but who nevertheless believe in me. This is both an encouragement for us and a mild rebuke of Thomas. Of course, this applies to more than 99.999% of all who have ever been Christians, as there were only a bit over 500 eye witnesses to the resurrection (1 Cor 15:4). Jesus is not encouraging blind faith. The Bible never encourages blind faith. Thomas had a boatload of evidence to believe in Jesus! In Acts 17:11 the Bereans are commended as noble because they heard with eagerness what Paul said, but then they checked out in the Scriptures to see if what he said was true. There is no honor in simply blind belief. All of us need to use our reasoning, otherwise our belief is shallow and in danger of being lost. Of course, faith, by its very nature, requires belief in things which cannot be “seen” (Hebrews 11:1), but such belief in things unseen is based on evidence which is seen. Even Jesus understood that his authority had to be based on evidence. He pointed to his miracles as the evidence that what he said was from God. You can see this more than once in the book of John. Also, in Deuteronomy 18:22, God told the Jews only to believe the message of a prophet if his predictions in fact came true. No, God does not encourage “blind” faith. You should continue to test your belief against the evidence. This is not a sin. I believe it will increase your faith. It certainly has worked that way for me.