I am one of those who P.Z. Myers is describing, except I learned creationism from and earlier generation of YEC’s, like Morris, Whitcomb and Gish. It wasn’t until I was an adult that I realized there was good reasons to believe in an old creation, and I read about the different Old Earth Creationist beliefs, Gap theory, Day-Age theory, and whatever else was popular at the time, and was wondering which one of them might be true. Then I re-read the young Earth arguments again and was convinced that the Bible definitely taught a young Earth…submit. So I did.
Fast forward. When I found out YEC definitely isn’t true and they are sometimes lying to defend it, the whole wall did fall, but I wouldn’t say it was a brittle wall. It is more concrete block wall that is very strong as long as it is intact, but if you knock a few blocks out of the foundation at the corner, soon the blocks above them will loosen and fall out too.
For me, it wasn’t evolution (biology) that was the straw that broke the YEC camel’s back. It was mostly geology. And then there is the dishonesty YEC’s will stoop to to rubbish science and discredit anything that breaks their Young Earth timeline.
Another problem that seems insurmountable for YEC’s is the “Distant starlight problem”. They have explanations to explain it away, none of them are good, but they successfully fool the average Christian into believing that YEC still might be true. It is a shame.