Taken out of context, John 20:29 is often used to justify faith without evidence. Greg looks at the whole passage to clarify the true meaning of the verse.
Source: Does Jesus Endorse Blind Faith? | Stand to Reason
Christians are often accused of taking a “blind leap into the dark.” However, my father Josh set out to disprove the Christian faith historically, but instead found the evidence powerful and convincing. So, when he became a Christian, it wasn’t a blind leap into the dark, but a knowledgeable step into the light. He placed the evidence onto the scales, and in his estimation, it tipped in favor of Jesus Christ as the Son of God, resurrected from the dead. You may be convinced by the evidence. On the other hand, you may find it wanting. But the claim that “faith is blind” simply ignores the biblical and historical evidence. In fact, only someone who hasn’t truly weighed the evidence could make such a claim. If you haven’t considered the evidence yet, maybe now is the time. — Sean McDowell (from, Clearing the Fog: “Christianity Doesn’t Need Evidence Because Faith is Blind”)
Source: Biblical faith is informed by evidence: 12 Apologetics Quotes ‹ The Poached Egg Christian Worldview and Apologetics Network ‹ Reader — WordPress.com