There are two very obvious gender differences. One males are, on average, far stronger than women. Second pregnancies are far more costly to women.
This means that men are far more likely to be interested in casual sex than women because they have far fewer things to fear from casual sex. Both because men feel less consequence from potential pregnancies but also because men have far less to fear about being physically overpowered.
It is not true for everyone, there's a cultural component as well, and there's nothing shameful or unfeminine about a woman interested in casual sex. But the fact the genders do have very different attitudes is backed up by virtually every study ever done.
You make some pretty bold and sweeping statements there. I would love to see the research that supports them. I can't seem to find any studies that support your claims, but since virtually every study ever done backs it up, it should be easy to provide some details.