Consent, as the primary criterion for sexual ethics, thinks too small. The careful, consent-seeking lover seeks to use his own strength correctly and responsibly. If a lover of this type finds that his strength is a little too daunting, a little too hard to wield cautiously, the solution is to find ways to limit his own power.
So we flense away the intimacy that sex serves, promising not to “catch feelings.” We take drugs or interpose rubber walls to prevent sex from bearing its natural fruits. The resident ethicist at the New York Times even offers a guide to fully eunuchizing sex, advising a man who hopes to open his marriage without endangering it: “This may be an argument for the sin of Onan, where there’s only yourself to fall in love with.”
In each of these cases, there is no abuse of another’s power, as when predators trample on consent. But there is an abuse of the power of sex itself, as we try to make sex small enough for two people to use it separately, safely.