Treating drunk sex as rape depends upon imputing malice upon the accused in conjunction with the accuser's withdrawal of consent following a return to sobriety, on the basis that a mutual and irreversible act which took place during the period of intoxication can be made no longer mutual by that later decision.
Treating drunken contractual agreement as a criminal act is contingent upon a second action taken by the accused following the accuser's withdrawal of consent upon a return to sobriety, on the basis that the second action constitutes fraud. That second action is the refusal to reverse a reversible action taken by the accuser while drunk - the surrendering of ownership of a financial asset in conjunction with the conditions of the contract. When a contract is simply considered void, and no second action has been taken by the holder to attempt to force the drunk signer to adhere to the contract, a crime has not been committed.
The thing that criminalizes signing a contract with a drunk person is not the act of signing the contract when consent was invalid, but the act of attempting to impose it after consent was withdrawn.
This is a condition which cannot occur in a circumstance of drunk sex, because once the sex act is over, there is nothing to return or enforce. There is no act of imposing an agreement after the agreement has been withdrawn. There is only mutual act which one party later determines to be a mistake made due to compromised inhibitions.
Taking an action due to compromised inhibitions and later regretting it is exactly like circumstances described in criminal law. It does not match up with circumstances described in contract law. The logic of applying contract law as being more analogous of the situation than criminal acts is flawed in its lack of consideration of the reasoning behind the involved laws.
Contract law holds that an individual cannot later be compelled to adhere to an agreement made while drunk, not that an individual is criminal for making an agreement with a drunk person. Treating drunk sex as rape holds that an individual is a criminal for making an agreement with a drunk person, not that an individual cannot later be compelled to adhere to that agreement - because following a mutual physical act, there is no further agreement to uphold. Where contract law criminalizes an attempt at imposition following a legally permitted withdrawal of consent, the feminist position on rape seeks to criminalize sexual activity that was not imposed after consent was withdrawn, but which took place before consent was withdrawn. It is an illegitimate attempt to impute malice where malice cannot be proved.
The feminist position on drunk sex is inconsistent with the analogy they are using. They could be correct in arguing that drunk sex doesn't constitute the beginning of a committed relationship, that it doesn't constitute an agreement to become parents (or owe child support - but they would never argue that), or that it doesn't entitle either party to expect future sexual contact with the other... but not that the drunken state of the participants makes one of them guilty of a crime, even if the other party later regrets her actions.
Criminal law holds that being drunk does not excuse an individual from responsibility for actions taken which affect other people. Treating drunk sex as not rape holds that being drunk does not excuse an individual from responsibility for actions taken which involve (and therefore affect) other people, even if the individual regrets those actions later on. Holding the accuser in a drunk rape case to the same standard as the accused in a criminal case involving drunk behavior is a correct and consistent analogy because both are contingent on dealing with the behavior of the individual at the time of the event, an area where the analogy using contract law fails.
*Edit to address an argument made in response to this point elsewhere, wherein an arrogant debater asserts that touching another individual is assault unless consent is given:
Not according to online sources of legal definitions.
Cornell clearly shows intent, imminent harm, and/or injury as factors which must be present for an event to be considered assault. Consent is not mentioned.
http://legal-dictionary.thefreedictionary.com/assault states the same criteria.
This is why, when person A threatens to hit person B, makes a motion as if to hit person B, or punches person B, those may all be considered assault, but if persons A and B bump into each other in passing on the street, while neither of them consented to the touch, neither is guilty of assault. One of them being drunk does not change that.
There is also the fact that an assault is not an act engaged in together by the victim and perpetrator, but one acted out by the perpetrator against the victim. A sex act is a mutually engaged action. Another example of a mutually engaged action is a boxing match. Person A and person B may engage in a consensual boxing match by donning the gear, entering the ring, and hitting each other until the match ends or one of them is knocked unconscious. If an individual drinks alcohol, then swings his fist and starts a fight, his participation in that fight is consensual even though he is drunk. If he is hit back and continues punching, he's participating in a consensual fight, not being assaulted, even if later when he wakes up with a massive shiner or messages on his phone about an embarrassing youtube video, he regrets starting the fight.
Were he female, and were the action she initiated a sex act instead of a fight, the result is the same: A mutually engaged interaction in which both parties actively participate, not a passive/helpless victim being acted upon by a perpetrator.
This is why cherry picking between contract law and criminal law does not justify feminism's position. In doing so, you're relying on treating women as helpless, passive objects without decision-making capability, and that's a wholly dishonest approach to the discussion.