Evil St. Patrick?

A lady came into the library today asking about St. Patrick. I retrieved information about the holiday and the man, trying to please this very grumpy woman. Nothing seemed to satisfy her and then after ten minutes of searching she clarified her request: she wanted to find "bad" things about St. Patrick so she could get her child out of celebrating that holiday at school.

This led me on a fruitless quest over the Internet trying to find a reputable source bashing the Irish saint. I found nothing until the woman spotted that St. Patrick was once a pagan in Britain before he was sold into slavery and came to Ireland. (Never mind the fact that this was about 400 A.D. and that region was full of pagans. Even if he was a pagan does that make him evil?) However, this information made her happy and she took it and left. My coworkers told me I should just wait for Halloween, she's here all the time then.