I think there's a lot of truth in that - NAGMALT, obviously, but some of the stereotypes about gay sexuality are rooted in reality. It's not exactly straight male sexuality without the moderating influence of women, but there's an element of that.
At the risk of stereotyping, if we see marriage as a long-term monogamous commitment that's normatively (though obviously not always) centred around mothers and children, same-sex marriage makes much more sense for women than it does for men.
We all know the phenomenon of the late-blooming lesbian, who finds herself single at 40, goes back on the dating market and somewhat to her own surprise hooks up with another woman, where she'd been completely heterosexual up until now. Maybe she was latently bi all along, but the point is that there's no male equivalent. Show me a straight man who comes out as gay in middle age, and I will show you a man who's been shagging other men all along.
(There's an obvious parallel with another thing men come out as in middle age.)
Now of course society has been moving for decades towards companionate marriage rather than a lifelong commitment based on raising children, and there are legal protections that go with marriage that gay men shouldn't be excluded from, and there are plenty of gay men who do want to be monogamous - it's just that the stakes are quite different.
The heart of the Dreher debate is that Rod sees marriage as a discipline, and specifically a discipline on the man. Sullivan has enough residual conservatism to see the point, but I think he's also realistic about gay sexuality. He wants Adam and Bruce to have the respectability and protection of marriage, but he knows there's a significant chance that Adam and Bruce won't allow marriage to get in the way of their swinging sex life. Whereas for Cathy and Diana it very probably will be a monogamous commitment.
I think Sullivan has a strong tendency to cakeism - in the case of marriage, he wants access to the institution but not at the cost of a discipline that many gay men will struggle with.
And I think his cakeism is on display too on trans. Of course he has trans friends he cares about, probably quite a few because he goes back to when T was mostly a subset of LGB, he wants acceptance for them, he probably accepts that transitioning was the right thing for them, he would like to think that the gay and trans orgs just need to ditch Strangio type extremism.
But he's smart enough that, on another level, I think he realises the cat is out of the bag on trans.