• She's more likely to cheat
  • We're predisposed from being cavemen to want to know who our partners are
  • Marriage Statistics!!!

All these justifications are weak and obfuscate the real reason:

It's gross. It's not attractive. It's like a revulsion in the pit of your stomach. Ew.

We do not ask women why they are sexually unattracted to short men, or broke men, or flamboyantly gay men. It's a preference, one that the majority of women happen to share.

The majority of men are sexually unattracted to women who have slept around. That's all there is it to it. This is the strongest argument possible, it requires the least justification, and it's true.