I think it becomes less grey when you think of it in terms of whether one would consent to sex when sober. i.e. if one of the parties has always wanted to have sex with the other, but the other is having none of it, and they use intoxication to get what they want, that isn't a grey area situation. That's rape. It is not a "no fault" incident.

If all parties involved wanted to have sex with the other party or parties, and the opportunity arose while they were intoxicated, that's not rape. Maybe still a little grey for all parties, and possibly not good judgment.

But, I think the grey area is much smaller than the instances of rape, and the fear some men seem to have of being accused of rape or similar for those extremely rare instances of "grey area" sex way overblown.

There was a study recently where participants were asked if they'd ever done various things, that effectively described rape. The same participants were asked if they'd ever raped anyone. The incidence of people who said "yes" to the behaviors that describe rape was much higher than the incidence of people who said "yes" to having ever raped someone. The participants thought those were "grey areas", but most of them were pretty clearly just rape.