Consent isn’t enough to guarantee that sexual behavior is moral. Adultery, the deliberate conception of unwanted children, the careless spread of H.I.V.—all could happen in consensual encounters.
Whoa, whoa, whoa. This is a myopic definition of "consent." Let’s break this down:
Adultery is wrong because it is breaking a very meaningful (and some would say sacred) contract between two people. If you you have sex with not-your-spouse without that spouse’s knowledge and consent then it’s cheating, adultery, and wrong.
"deliberate conception of unwanted children" – huh? How could it be deliberate if its unwanted? Even if you rephrase this as the "irresponsible conception of unwanted children" the problem is that you’re presumably harming a child by carelessly bringing it into the world, therefore harming a third party.
If you have HIV and you fail to inform a sexual partner, that partner has not truly "consented" to the act because they were insufficiently informed. If both parties know yet for some reason fail to adequately protect each other, they’re placing a burden on others – future sex partners of the at-risk partner, their friends and family, the social institutions that will bear the cost of their care.
In all of these cases, the reason consent between the individuals committing the sex act is insufficient to justify them morally is because they are generating harms to third parties. If you own a house next door to Conor Friedersdorf’s house, and I buy it from you with the intent to knock it down and built a giant coal-fired power plant there, and you know that and are fine with that, and there are no legal prohibitions, that’s still not a moral thing to do because it’s not very nice to Conor.
Friedersdorf does a good job defending consent, but I would argue his definition of "consent" is insufficiently broad.