Prenups really kill the mood. "I love you til death do us part"—but if you turn out to be a bitch I'm totally cutting you off.
Lots of aspects of marriage, and society in general, don't stand up to rational scrutiny. We're not just fallible, we're downright wooey. That doesn't mean these institutions are valueless or predatory—just that the human experience is not primarily about the rational.
I could see this one either way. Maybe if you're a billionaire, the prenup makes it clear you're marrying for love rather than profit. From down here in the sub-sub-sub-billionaire world, it doesn't look that way, but who knows? Lots of things are different "at scale."