See, I don't really agree with you not being the same person under the influence of alcohol or even many other drugs. It's still you, filtered through abnormal brain chemistry but everything underpinning all your decisions was still your self. You might as well argue that you're a different person while under the effects of a surge of naturally produced hormones, for example. Unless it causes some sort of psychotic break that detaches you from normal reality, you're absolutely the same person.

Your example of getting someone drunk to take advantage of them is a bit different from having someone do dangerous/stupid shit by themselves though, since it introduces another actor. A bit off topic, but should it maybe be the case then that the other person should also be required to be able to recognize the other party's disadvantaged state? Is that not just straight up abuse otherwise?