I think the weird focus on “edge” cases of “mutual intoxication” is sort of missing the point.
First of all, the idea that two people are just commonly at the same level of impairment all the time is stupid. Especially because impairment is non-static, just because you are too drunk to drive, it doesn’t mean that you might not be sobering up. Conversely, just because you’re currently below the legal limit, it doesn’t mean that you’re not steadily absorbing more alcohol already in your gut. Figuring out whether two people are at the same level of “drunkenness” (which let’s face it, is often a social assessment with legal benchmarks for things like driving) is frankly more impossible than possible.
By and large someone is always going to be “more drunk” and oversimplifying to make the less drunk party more responsible in all cases (despite the fact that being drunk affects your perception of social cues), doesn’t solve any problems. However it also doesn’t solve any problems, and it creates new ones, to stand around pretending that we should all throw our hands in the air and pretend that alcohol simplifies things (instead of complicating them) if both parties are so drunk that this is a question. Here’s a good guideline: “Buzzed,” (again, a social rather than medical distinction) while not a legal distinction and a concept that will get you in trouble while driving, implies the ability to give responsible consent. People do drink to reach a stage of relaxed inhibition, especially in romantic contexts, and it’s about mustering the courage to do what you want rather than to force yourself through some ordeal. I think most people would agree that the warmer feelings and looser flow of conversation don’t indicate that a person is inebriated and beyond consent.
An aside: “Informed consent” is somewhat meaningless in this context, and is mainly the purview of the medical establishment and institutional review boards. It’s a great phrase, but it just doesn’t apply here, because it’s not clear what people should be “informed” about. Certainly there’s STIs, but that’s just plainly not what’s being discussed here. So, let’s avoid that phrase. I prefer “responsible consent” (as in, “capable of giving a meaningful response”) or just “consent.”
Beyond this sort of warmed-up and relaxed state, lies a territory that people should just avoid, unless they know the person fairly well. If in doubt, wait until later. People who genuinely want to sex you don’t typically change their minds about your overall eligibility. The context of two people with an established sexual relationship getting drunk and having sex is different from the context of someone you randomly meet at a bar. The former is often based on a foundation of real knowledge, and expectations that can be set explicitly, and the latter is really a gamble that you’re reading all the signals right. The thing about being an adult is that we will forgo opportunities to avoid unnecessary risk. Why should we pretend that adults who fail to do this with sex are entitled to a different set of standards than they are in just about every other activity?
This is why the “mutual intoxication” scenario is such an annoying trope. Not because it doesn’t happen, but because it’s really founded on the supposition that there is no risk involved, when in fact the risks are often greater and more obvious. This also ties into various other problems, like the manner in which we talk about this kind of rape as being a function of “regret” rather than acknowledging that you can take advantage of people who are not necessarily blackout drunk. A bartender I know will “cut people off” without telling them by making their mixed drinks virgin and tossing a little bit of alcohol on top for flavor. He does this all the time with people being none the wiser, and if he charged for it, it would be deeply unethical, but he just gives it to them on the house and it’s a benevolent act. Same thing with “tricking” your drunk friend into giving you their keys. Another example of a benevolent act that no one will fault you for. Yet often, you yourself can be drunk while you do this! Sometimes just as drunk, but you got an inkling of something wrong happening enough to act. People who are drunk still have agency, but how that agency gets asserted and whether the other person can put up meaningful resistance is complex. This is why it’s just a bad risk, and why it can not be a problem nine times out of ten, but come to bite you in the ass on the tenth time.
Finally, and most importantly, this sort of thing is comparatively rare. Most cases of people who are too inebriated to give consent are very clear, and often will involve people who raise weak objections because that’s all they’re capable of. Women who have sex while drunk in the sort of mutual drunkenness scenario often described and simply regret it later don’t often even try to pursue the matter with the justice system. Not because they won’t be believed (though this certainly happens), but because they will acknowledge that they made a decision to give consent that they now regret, and they’re not sociopaths. In other words, a rape didn’t happen or it was so borderline that it’s not necessarily attributable to anyone behaving badly, and the woman did not immediately turn into a vindictive harpy. Let’s pause for a moment to ask ourselves why people think this is the rule rather than the exception.
