I don't think 'incapacitated' is the word in question. It is the word 'unwanted' that is problematic.
If you go to a store and ask for a bottle of poison, then take that poison home and decide you don't really want poison after all, did the store clerk poison you? According to the logic in the definition used to describe rape, that would have been a poisoning.
No, but I can see how saying that would let you pretend to feel better.
Look, I've watched drunk college aged guys try very hard to pick up girls who were very nicely, politely turning them down and then being escorted away from the obnoxious drunk guys hitting on them by sober or less drunk or at least less obnoxious guys who could clearly see that the girls were not interested. But the drunk guys remained unconvinced that those girls didn't 'want' them. Loudly insisted that the girls wanted them. Had to be prevented by others from pursuing the girls who left the party because of the obnoxious drunk guys.
Drunk people are not always very good at being able to determine their own level of drunkenness, impairment, capacity, etc. They still are quite able to force themselves upon other people who are not interested in their attentions. Sometimes, this includes sexual assault.
Drunk people are also pretty often ineffective at standing up for themselves, assessing a potentially dangerous or unwanted situation, or fending off an unwanted kiss--or unwanted sexual assault.
Drunk people are not allowed to legally drive automobiles or motorcycles. If they sign contracts or marry while inebriated, the contracts can be voided if challenged because the law recognizes that they are not capable of making decisions or effectively advocating for themselves.
I've seen drunk guys attempt to force themselves sexually upon girls who were drunker--to the point of being unable to stand or understand what was happening. I've seen sober guys attempt to force themselves upon drunk girls. I've heard a lot of girls try to diminish the impact of being sexually assaulted while they were so drunk they were passed out--they-the girl--'shouldn't have been so dumb.' I lost the friendship of a guy I had really liked after he told me that he pushed a girl into having sex although she told him no, repeatedly. He didn't think he did anything wrong.
What I haven't seen or heard is a girl --or a guy--claim to be raped after mutually consented sex, even if one or both was drunk. I am sure that happens but not