Really?! I never had the slightest issue understanding this. Why not ask them?
In my experience, nearly all such people have simply been abused in the name of religion or by religionists in the past. It is likely that millions of children were sexually abused by Catholic priests alone. France is one of the few places to try to come up with a number, and theirs is 330,000. But it turns out that statistically an individual Catholic priest is no more likely to molest kids than any other religious figure...
Is it really any surprise that some of these people show up to your column to complain about religion? I certainly would!
(My mother was a Christian, but one who exemplified the best virtues of Christianity, even while she herself did not, I think, believe in any of the miraculous parts, so it's only as an adult I started to believe that religion is generally a bad thing, but I don't feel the need to argue this point, and man, it would be nice to believe that my consciousness might live longer than this no-longer-young body, so who am I to take away people's consolation?)