Yay, ethics of influence and seduction, one of my favorite subjects. I'm still figuring out my thoughts, so I would appreciate it if people tell me if I'm making incorrect assumptions.

First, I'll state that I prefer the terms "unethical influence" and "unethical influence" to "manipulation" and "non-manipulation," because people use "manipulation" to mean too many different things.

Second, in ethical discussions, we should distinguish between things that would be a good things to do that aren't morally required, and things that are morally required (Kant called these "imperfect duties" vs "perfect duties"). Also, we should distinguish between ethical courses of action, and empathetic courses of action. There are lots of cases where there's an action that's a good and empathetic thing to do, but actually requiring it as a perfect duty would screw everything up.

Physical coercion forces you to do something that you don't want to do, don't enjoy while you're doing it, and regret doing afterwards.

There is clearly a perfect duty against physical coercion, and that duty applies even if someone happens to enjoy what you are doing. An example of that case up when Roissy (a pickup blogger who built up a large following, but isn't actually typical of the seduction community) condoned slapping women in arguments because it could "turn them on." I argued that even if a certain percentage of women are turned on in that case, slapping without consent is unethical on both deontological and consequentialist terms. That thread has since been deleted, or I would link to it.

Hitting someone nonconsensually violates their rights from a deontological perspective. From a consequentialist perspective, the expected value of a positive reaction occurring is negative.

Emotional manipulation causes you to do something that you didn't want to do before, and regret afterwards -- but you may like it in the meantime.

Is it empathetic to avoid people regretting your forms of influence? Yes. Is it an imperfect duty to avoid buyer's remorse? Probably yes. Is it a perfect duty to avoid influence that could create buyer's remorse? Probably not.

This moral principle (as I understand it) is a bit too broad. It catches many things that we would actually consider ethical. A bit part of the problem is that it doesn't account for uncertainty about whether buyer's remorse will occur; I'm not sure what levels of uncertainty you are imagining, so the following analysis may reflect my interpretation of what you wrote better than it reflects your actual views.

Let's say you want a friend to come to a movie with you. Your friend initially protests, but then you hype up the movie. Your friend decides that it sounds cool, and comes with you. Afterward, the friend enjoys the movie, but afterwards decides that it wasn't worth the cost of admission.

By your criteria, this was "manipulation," but I don't think anything untoward has occurred here. Agree/disagree? We are, of course, assuming that your friend comes out of interest, not merely to make you happy. You don't know in advance that your friend will decide that the movie wasn't worth it.

The third option is "try it, you'll like it." The person didn't intend to take the action before, but she wanted to do it at the moment she acted, and she was glad she did it afterwards. I don't see a moral problem with this. It's influence, but it's not harmful.

But this sort of influence can sometimes result in people doing things that they regret; I'm having trouble reconciling it with the other principle you articulated.

Now, what if you knew that your friend probably wouldn't find the movie worth it, and you dragged them along anyway? That's falling into the category of unethical social influence, and perhaps that's the scenario you are proscribing. But if you believed that they would enjoy it, and you turn out to be wrong, then arguably you've done a good thing by taking your friend to a movie that they might plausibly like, and that they believed that they would like based on information that you provided them... even though you were both wrong.

When influencing people, we must assume by default that people know their preferences better than we do. You must give primacy to the version of your friend that wants to see the movie now after you've told them why you think it will be great, rather than to the version 5 minutes ago that didn't want to go out of the house.

People usually know more about what they will or won't regret, and what risks they are willing to take, than we do. So if someone is willing to engage in a certain activity with you, that's pretty strong evidence that it's a good risk for them to take from their perspective. The fact they initially didn't want to in the past is evidence that they might have buyer's remorse, but that evidence is much weaker than the evidence of their preferences in the present.

Of course, if you have some information that someone might end up getting buyer's remorse that they might not be aware of (like the product you are selling is defective), and it's information that you believe the other person doesn't have access to, and shouldn't be expected to figure out for themselves, then influencing them starts becoming unethical. Perhaps that's what you mean when you say:

Influencing someone to take an action that you know she will regret afterwards is manipulative.

Yet it's actually rare that you "know" in advance whether or not someone will regret sex; in most cases, you really only have a guess, and so do they. By default, the informational asymmetry about whether the other person will experience buyer's remorse favors the other person; their guess is probably better than yours about how they'll feel later, and you shouldn't try to do their thinking for them unless you know something big that they don't.