Gotta keep yourself clean down there for your government mandated rape victim... Er uh... I mean "enforced monogamous partner"
The state isn't the only or even the best way to enforce things. Culture and society are the things that enforce many cultural norms.
Now maybe you might ask "why should society enforce monogamy?", but to me the real question is, "do you hate most women and most men?"
If we don't enforce monogamy at a societal level, the alternative seems to quickly become powerful men acquiring massive harems, and many men never getting a chance to be in a sexual relationship of any kind. The consequence is that the women are treated like garbage because they're just one of many in a powerful man's harem, and many of the men go crazy and become increasingly extreme in an attempt to secure their future. We see this in some African countries where old men treat their many wives like trash and young men are ruthless and violent because they have no chance of participating in a key piece of the human experience through normal means.
"The child who is not embraced by the village will burn it down to feel its warmth."
