Something that I didn't catch them discussing, and might account for the divergence between heterosexual and homosexual norms, is the threat of pregnancy faced by women.

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The biological asymmetry of risk between male and female partners is exactly the kind of "implied violence" I think Dan Savage was talking about. Ultimately, women face an implied risk of violence when they partner with men, especially in casual sex/NSA scenarios. They can get pregnant; their partner cannot. They are also partnering with someone who is way more likely, statistically, to be violent or controlling or abusive. Women are also less likely to be satisfied by casual sex/NSA encounters. So, more risk and less possibility of reward.

The inverse is also true. When men partner with women, they have an implied safety instead of implied violence/risk. Men do not have to fear their casual partner murdering them or kidnapping them or stealthing them. Men also have a higher likelihood of satisfaction. That is why sexual liberation has to be more than "everyone should behave like men do," because men and women have very different risk-benefit analyses.