Batman’s a bit of a masocist.
On one hand, nothing pleases him more than making a crook swear to him. It’s what he gets up for in the morning. Some may call it a simple pleasure but those are the kind that Batman likes best.
But, on the other hand, swearing is bad and Batman hates things that are bad. A bad thing killed his parents when he was young and he’s never been able to keep himself from judging all bad things from that one event. So he hates swearing.
This is yet another example of the many complicated issues Bob Kane incorporated into his classic character, The Batman.