Casual sex in itself isn't evil, but there are severe consequences to such a lifestyle, especially for women.
The issue is that people, again especially women, are either clueless or deluded in accepting that there are consequences --mental, physical, emotional-- to being a "lock that any key can open".
And, yes, it is worse for women because of a woman's biological role/how being a binary gendered reproductive species works. They just want to deny it because mumble mumble "patriarchy" and mumble mumble "finding herself".
Their rhetoric of "past doesn't matter" and "normalize dating sex workers" falls apart when the man they're seriously interested in, and he's interested in her, loses interest once he discovers her past/history, typically relegating her to "casual fun" than "serious relationship" status.
All we have to do to stop this behavior is to stop subidizing it.
You want to be a single mother? Fine pay for it yourself, you have complete control over your pregnancy? Ok fine then having a kid is a unalateral decision one your paying for. Get rid of Alamony, get rid of child support and stop giving welfare to single moms and this shit would all come to a crashing halt fast.