This assumption seems based on the idea that affirmative consent is limited to a dry mechanical context when the actual concept of affirmative consent is much richer and not at all foreign to how we understand consent in most other contexts and how we live our lives and even how we enforce our non-sex crime criminal statutes.
We understand that when people are consenting they are indicating that they want something or are willing to have that something and that any expression of agreement is free of duress. If a stranger grabs you and says, "Gimme your wallet," we understand that tossing your wallet is not an expression of affirmative consent. We understand the threat nullifies affirmative actions even though the threat is not spoken. We also understand that duress is judged by the perception of the person who complies. If a mugger says, "I would have run off after another sucker if he said no," we understand that this doesn't turn the interaction into a consensual one even if this mugger is being truthful.
In short, there's nothing inherently oppressive about the concept of affirmative consent. If sex was truly consensual from the perspectives of all involved then nothing changes under an effective system of affirmative consent. However, when people approach sex the way that mugger approaches other people for money then this concept will not be one they will want to embrace or want to see used in the enforcement of sex crimes statutes.
When people who resist looking at consent from the perspective of the other person claim that determining what the other person wants or will freely agree to sexually is a hopeless mess, the response they often get is for them to stop guessing and to explicitly verify consent. This is often taken as meaning that the only way to determine affirmative consent is repeatedly make specific verbal requests and to get specific verbal agreements.This isn't true, and as the mugger example shows, asking a question and getting a verbal positive response doesn't always mean there was affirmative consent.
We understand why this is so in other contexts but in the context of sexual interaction this is often presented as proof that affirmative consent is unworkable. An easier set of terminology for how affirmative consent works to determine the dividing line between truly consensual sex and truly non-consensual sex and which doesn't confuse people with false positive responses are opt-in and opt-out.
Affirmative consent is a serial opt-in system that allows an opt-out at any time and which always returns to opt-out status whenever someone is not capable of opting in or of freely expressing the desire to opt out. Affirmative consent is non-transferable. If someone wants to opt-in to something which by default is opt-out they need to clearly negotiate their personal boundaries.
This is clearly different from the mere presence of the word yes. This is a standard which maintains a person's freedom and requires the unending respect of other people's freedom. Respecting other people's freedom at all times is more complex than continuing until a no or taking a yes as a blank check, but this complexity is not a valid excuse for failing to respect other people's basic human rights even during sexual activity.
No social status or label nullifies the need for genuine affirmative consent.
Opting in doesn't require a document as many opponents of affirmative consent claim but it does require a process of respectful learning. With an opt-in/opt-out system there is no guesswork or assumptions about consent existing in the absence of an obvious opt-out. Mixed signals always means the opt-in hasn't happened. In this system a document freely signed giving another person fixed rights will always be superseded by the right to opt-out and any document not freely signed is meaningless.
For anyone who has wanted sex but who has not wanted to opt-in, this system may mean being prompted for explicit feedback from someone who doesn't want to risk being on the wrong side of the law by reading too much into passivity or it may mean others will simply walk away. Those who cannot bring themselves to opt-in may not get the sex they want. This is a better alternative than allowing rape so that all those passive willing people get sex every time they want it.
Another argument against an affirmative consent standard is that the ideas behind this model cannot be integrated with the law. But they already have been in some jurisdictions.
Minnesota's criminal statute uses this affirmative definition of sexual consent:
(a) “Consent” means words or overt actions by a person indicating a freely given present agreement to perform a particular sexual act with the actor. Consent does not mean the existence of a prior or current social relationship between the actor and the complainant or that the complainant failed to resist a particular sexual act.Without (c) most rapes would be treated as if they were legal and would give rapists a clear path to getting away with rape.
(b) A person who is mentally incapacitated or physically helpless as defined by this section cannot consent to a sexual act.
(c) Corroboration of the victim’s testimony is not required to show lack of consent.
Since the complete working of the criminal justice system go far beyond what is written in the statutes this change in definition is just a beginning, but we need to start and keep moving forward with respect for the basic human right to have our sexual autonomy respected at all times.
So much of the history of how people and the law have looked at sexual consent have viewed a person's actual willingness as irrelevant. This must change if we are serious about preventing sexual violence.