I want to want to have sex with you, but I never want sex unless I’m high or drunk. I can’t relax and I don’t enjoy it. But look, I’ll start drinking, and hopefully there will come a point where my inhibitions are sufficiently lowered and I’m relaxed enough so that we can go ahead. But realize I’m not consenting right now to have sex with you later, I’m simply telling you that I’m making the choice to drink in the hope that I will come to want sex later on. If that happens, I’ll let you know, but it might not.This person then starts drinking, ingests some ... amount of alcohol (i.e., past the point at which under normal circumstances you would consider it wrong to have sex with them), and then tells you they are ready to have sex with you." Is there anything wrong with going ahead? A bunch of assumptions we're supposed to make come next--have a look over there.
Let's make this more manageable by putting it all in the third-person. John wants to have sex with Mary. Mary merely wants to want to have sex with John, and makes the speech above. The odd thing about the speech is that at first, Mary more or less tells John that she does want to have sex with him, but she's simply not ready yet. That seems to be the import of her telling him that she has to be high or drunk to want to have sex. In essence, she's saying to him "My reluctance at the moment has nothing to do with you. In principle, I do want to have sex with you. But I want to be able to control whether we stop or go, at every point in time." OK, fine ...
But then Mary shifts gears, telling John he has to wait for consent that may or may not come later on. "But realize I'm not consenting right now to have sex with you later." This sounds like more than wanting to maintain moment to moment control. She actually wants John to think there's been no consent yet, and consent may come later on, at the point when she's drunk -- or may not.
Well, no! Imagine it's like this--
John wants to sell his motorcycle to Mary. Mary wants to want to buy, but she's nervous about it, so suggests they go to a bar, where she will have a few beers in the hope that she will start wanting to buy the motorcycle. She's adamant that consent for the sale hasn't been granted yet, but says consent may (or may not) be given in the bar.John should certainly decline this plan. You need mutual consent for a major sale, and he won't be able to secure it. Likewise, you need mutual consent before sex, and John won't be able to secure genuine consent from someone who's inebriated.
Now, there are times when we don't really need mutual consent, because the activities in question are too trivial. Here's another John and Mary story--
John wants to go on the roller coaster with Mary. Mary only wants to want to go on the roller coaster with John, but doesn't want to. She suggests they go to the Green Beer Booth first. She has a few beers, then says "let's do it!"Fine. He doesn't have her consent before getting on the roller coaster with her, but doesn't need it--the activity is too trivial.
I take it that in our society we see having sex with someone as more like buying a motorcycle from them and less like going on a roller coaster together. That's why the drunken willingness that's sufficient in the roller coaster scenario just won't do when the issue is whether to have sex. Is that silly or irrational? Hardly! Sex involves bodily penetration, risk of pregnancy and sexually transmitted diseases, emotional risks, and so on.
Poor Mary and John! If she really can't consent to sex without being inebriated, I think she's going to have to remain celibate. And he's going to need to find another partner.