A couple of quotes from Mark Twain - I'm sure Star Stuff will have given these:
"Faith is believing something you know ain't true."
"It ain't the parts of the Bible that I can't understand that bother me, it is the parts that I do understand."
As the Enlightenment occurred, it became increasingly difficulty to "have faith" because of the first quote. During the First and Second World Wars, the news media began, for the first time, to be able to describe, in detail, with immediacy and to millions, how bad people could be to each other and, from 1945 onward, the world found itself populated by people who abhorred the savagery and inequality that had been preached by our elders and betters and refused to accept that there were gods who had control over our lives - we realised that mankind controlled his own destiny and that of others.
Prior to the Enlightenment, there were few answers to the big questions other than "God-did-it." and the brain, thus misled and under-informed, was the perfect vessel in which to hold "faith". We needed explanations and absent the real answer, anything would do.
So, if faith is a requirement for god then is our brain a design flaw?
The question is the wrong way round. For me, it should be, "Now that the brain has real information available to it, why do people still believe in gods?"