First off, you really really shouldn't be having sex with anyone that does give enthusiastic and vocal consent unless it's otherwise been discussed beforehand (sex while a person is sleeping, bondage scenarios where a person is gagged and/or unable to otherwise signal their discomfort, unprotected sex especially).
Second; if someone is legitimately drunk, they're in an altered state of consciousness and they will almost definitely react to situations and stimuli differently than they would if they were sober. They may do things or be suggestible towards doing things they may not normally consent to (I've heard a ton of stories from guys doing anal with their gf/wife/SO while one or both of them were drunk and wouldn't normally consent to it while sober and I personally think that's morally reprehensible). They may remember these things later, regret them, and it can be a huge source of shame and embarrassment for that person which can have a multitude of negative effects on them and their psyche.
As a rule, I don't have sex with anyone that's had more than three shots of liquor or six light beers - and even then only if I've had sex with them before while they were sober and have established a trust and general idea of what they are and aren't okay with. I'm talking about someone I've been in a 1+ year relationship with.
It really comes down to the consequences of their actions as well as whether or not they were the sole party giving consent to their actions; if you're drunk and choose to drive, it doesn't matter if you regret it and "only did it because you were drunk" because you chose to make that decision and it could severely harm or even kill yourself and other people. That speaks volumes about your decision making capabilities as well as the value you place on your own life as well as the lives of others - and you made that choice.
If you have sex with someone that's drunk, even if they enthusiastically and vocally consent to it, you were of sound mind and body and they were not. You took advantage of them being in an altered state of consciousness. Regardless whether or not they initiated it or you did, you should have the character and decency to decline their offer of sex because you don't and (generally speaking) can't possibly know if it's something they would normally want sober.
The only reasonable excuse would be if you were married to someone and had sex with them while they were drunk, and only then if it was a form of sex that they'd consented to previously while sober and you didn't take things farther than you had while they were sober. Marrying someone is saying publicly and making a legal record of your trust in them with your life. They can make decisions for and about you if you were otherwise incapacitated and so it's implied consent for sex regardless of many different possible scenarios.
Driving drunk is a poor decision on the part of someone with an altered state of consciousness in flagrant disregard of danger, safety, and the value of their life and the life of others. Having sex with someone that's drunk when you're also not drunk means you (as a person of sound mind and body) could have said no and didn't; whether you did it for the right reasons or the wrong reasons, whether or not there was prior or present vocal and enthusiastic consent, you are at fault because you knew they weren't sober and that you were and took advantage of their altered state of mind.
I've been in relationships with women that liked it when I would initiate or have sex with them while they were asleep. We'd discussed it beforehand and laid out when it was and wasn't appropriate for me to do so and the manner of conduct in which I was expected to operate. If they went to bed with no underwear on and no pants/shorts on, it meant that sex with them while they were sleeping was perfectly fine by them and that they gave me consent to do so even though they were in an altered state of consciousness so long as I stopped if they woke up and told me to stop or were clearly being upset by my conduct with them while they were asleep. Even though I could initiate while they were in an altered state of consciousness, if they wanted me to stop that almost always happened once they'd woken up during the act and were thus in a normal and sober state of mind or expressed a lack of consent or a desire for me to stop while they were still asleep and in an altered state of consciousness.
Someone that's drunk can't "wake up". They can be taken advantage of while conscious because they have lowered inhibitions and cannot express themselves as they would normally, while I (or you) had a sober state of mind and thus more control over our actions and that drunk person.
Seriously. Do not have sex with someone that's drunk. Doesn't matter if they're literally begging you to, don't do it. If you do then you're taking advantage of them.
I practice BDSM with my partners. We establish a groundwork of what is and isn't okay as well as multiple different ways of making sure we both know if a person wants sex to stop or slow down or resume. I get written and sometimes notarized consent for specific acts and the manner in which they are consented to be performed. Generally speaking I don't initiate sex with my partners unless they're sober and literally begging for me to have sex with them. There's no mistaking that they want it and how they want it and the manner in which they will express a desire for me to stop or slow down. That's not the case if a person is drunk in 99% of situations, and for that reason it's wrong.