Think about what you just said.If a man has sex with his wife while she is intoxicated and she hasn't given him permission....that is considered rape under the law.
If the wife is drunk, how does she recall if she gave the man permission or not? At what degree of drunk would she recall? If drunk, is she the best witness to say she didn't give the man permission? Do you think a jury would believe a drunk wife over the word of a sober husband?