What's so bad about blind faith?

"Blind faith" is a pejorative label. When atheists talk about Christian faith, they define it as believing something without evidence, on insufficient evidence, or contrary to evidence. 

Atheists don't usually begin with a theological or philosophical definition of faith. Rather, they begin with their belief that Christianity is errant nonsense, so you have to be irrational to be a Christian. The atheist works back from his view of Christianity to come up with his own definition of faith. Given his view of Christianity, faith must be believing something without evidence, on insufficient evidence, or contrary to evidence.

Christian philosophers, apologists, and theologians rightly reject that definition of faith. Of course, some professing Christians are guilty of blind faith. They simply believe whatever they were taught–the historical accident of whichever denomination they happen to be raised in. But it's unfair to assess a position by its least competent representatives. 

Blind faith is groundless faith rather than grounded faith. Uninformed faith rather than informed faith. 

In Scripture, the distinction between faith and sight is generally the difference between firsthand experience and testimonial evidence. 

However, in this post I'd like to be contrarian. Suppose, instead of repudiating blind faith, we embrace it but develop it in a different direction. 

Consider literal blind faith. Suppose I'm born blind. I have a sighted brother 2 years my senior. We grew up together. Day in and day out for 20 years. 

I rely on my brother to help me navigated my way through life. He's my eyes. Because I'm blind I see the world through his eyes. 

I have no direct evidence to back up his observations. I can't compare his observations with my own, since I'm blind. 

However, I have direct evidence that the observer is trustworthy. I have direct evidence that my brother can be trusted, which is, in turn, indirect evidence for what he tells me. For twenty years, my brother has guided me and protected me. He always looks out for me. My faith in what he tells me he sees is (literally) blind, but my faith in him is deeply informed. 

Moreover, although I can't see what he sees, his guidance and sight enable me to discover the world by other means. He says "touch this!" "Don't touch that!" "Taste this!" "Don't taste that!"

Suppose he drives me to the beach. I can't see the road. I can't see the signs. I don't know the route or the landmarks. 

But once we get to the beach, I have other ways of sensing the beach. I can feel the sand under my bare feet, feel the water, hear the surf, taste and smell the salty air.

My (literally blind) faith in my brother's verbal descriptions is an entry point. By taking what he says on faith, that puts me in a position to explore the world and find things out for myself. Faith is a necessary entry point. But the end-point is knowledge. Thanks to my brother, I can experience the beach. I rely on his eyesight to take the first few steps, but once I'm there, faith gives way to personal experience. 

Dropping the metaphor, when I pray, that's an act of faith. Suppose on one or more occasions I receive an unmistakable answer to prayer. At that point faith passes into sight. But I wouldn't arrive at sight if I didn't begin with faith. Knowledge is the final destination, but faith is the departure gate.