Why is being intoxicated a valid argument against consenting to?
Because in the first two cases it can be reasonably argued that you were being taken advantage of, and/or that you were the victim. However if you get drunk and commit a crime you werent being taken advantage of, and you were not the victim. Also then you have the issue with someone having 3 beers and then shooting his wife and claiming he cant be guilty of murder because he was drunk at the time.