Firstly I think the premise that rapists don't believe they have to obtain consent is a false one in many cases. To use an example of a poster further up this thread I think they know full well that it's not OK to have sex with a drunk women. I think they enjoy knowing what they are doing is wrong and will do it anyway. So I don't think that this group of people will be changed or deterred in this sense.
I think the Ched Evans case indicates differently - there was certainly a sense in the comments made by many men and women about the case that the fact that the victim was drunk was not only seen as not being a problem, but as a justification for what Evans did- as in, she was drunk, what did she expect? I think underlining the fact that being drunk isn't a crime but rape is is important. I do believe there are plenty of opportunistic rapists out there (my own rapist being one of them) who will rape because they know that society won't blame them for it. If it's made clear that drunkenness will cause suspicion to fall on the man not the woman then I think that will reduce opportunistic rape. If one rape is prevented, it's worth it.
Secondly I don't see how it helps people who were raped when drugs or alcohol were not involved. How on earth do you prove that you didn't say yes in that situation? It's still a he said/she said type situation.
Witnesses, or CCTV, as in the Ched Evans case.
Also where is the line in the sand regarding intoxication on alcohol? How drunk is too drunk? Who decides that, is it on a case by case basis? Does it depend on how much a person usually drinks. It's unlikely a women/man will be able to prove how drunk they were at the time of their attack unless they get a blood test straight away.
Again, witnesses can say if a woman was incoherent, or stumbling. That would make a good case for severe intoxication. The line would have to be determined by the jury.
What happens in a case where the rapist is equally as drunk as the victim? Will courts begin to argue that if a victim can be too drunk to consent a rapist can be too drunk to know what they were doing?
Being drunk, or "not knowing what you were doing" is not a defence, except in cases where there is a medical condition (such as sleepwalking) that the person can't control.
It would be interesting to know if there will be a sort of amnesty in the legislation for women who abuse drugs and illegal substances. A lot of very vulnerable women use drugs regularly and are more likely to be raped while unable to give their consent because of their drug use, but will they be able to admit that without risking prosecution for their drug use? Being high on drugs isn't a crime - possession is.
I'd feel more positive about it if there was something being done about the roll of pubs and clubs in all of this. It's them that are supplying already drunk women with enough alcohol to make them incapacitated in many cases. What happened to landlords being responsible for their patrons?
It is not the duty of publicans to prevent rape.