Hmm. See, I think that we get the thin end of both wedges, actually.
Yes, back in the day women got told casual sex was bad, and that was the end of it. But now it's more 'all women must be up for casual sex or you're frigid, but not too up for it because that's slutty'.
I suspect I'm coming at this from a different angle from others because at the moment I'm hearing a lot about pressure on women (esp young women) to have casual sex and it's pissing me off.
If you look at clubs, and promotions, especially for student nights, there's a lot of emphasis on casual sex - and the implication women should be up for it. If you walk around a university campus, same thing. I live in a fairly studenty area and I teach undergrads so I see a lot of it from a slightly distanced perspective and, honestly, the extent to which that sort of emphasis is used to pressurize, bully and abuse women is horrible.
I'm not cheerleading monogamy or traditional marriage, btw, just think that the view of casual sex as outlined in the OP is a bit rosy-tinted. I can believe it works if you're sure of yourself and, well, a bit more mature. But a lot of the damage seems to get done to women who're quite young.
And don't get me started on the truly horrible blokes I know who prey on younger women, tell them open relationships and casual sex are the best thing since sliced bread, then end up with a free live-in fuckbuddy/domestic help while they continue sleeping around.
I honestly don't think there is any kind of relationship set-up that isn't open to abuse. That's because some people are nasty, abusive fuckers. You don't suddenly step out of the patriarchial framework by having casual sex.