If you love your fianc�(e) WITHOUT conditions, why sign a PRE-NUP?? Debate?

I always ponder, why people sign pre-nups if they profess their love for each other? At least, from most matrimonial laws I know, the law allows each partner to keep their individual ets pre- marriage, which is fair. But why start thinking of divorce-that's what pre-nup is??? I'm looking forward to enjoy this debate!