If you review the original post, it's not his wedding. It's his friend's. Are you really arguing that, after the bride and groom have decided what the wedding party will wear, someone should wear something different, especially without asking them? Would the same rule apply if, say, the wedding started mid-afternoon and, despite the couple's desire for everyone to wear dinner suits, the OP showed up in a business suit instead? It seems from the above that you would say that, since his choice is more correct, their objection would be their problem, not his.
I think the OP did nicely by asking about the shoes and getting the go-ahead for wearing his PAs.