> If you have the power to make a better outcome happen 90 percent of the time versus 80 percent of the time, you choose 90 percent even if you are wrong some of the time

I don't see how this leads to your having to get my consent to make me like vanilla instead of chocolate. If you believed making that change in me would "make a better outcome" with 90 percent probability, by your logic as stated above, you would be justified in doing it without my consent. But you said that case requires consent "absolutely". I don't see how your stated rule does that.

Perhaps I should describe my position on this in more detail. My reason why you should not change my brain without my consent, whether it's to cure my brain cancer or make me like vanilla instead of chocolate (actually in my case it would be the other way around), is that you are not the one who has to live with the consequences; I am. So I should be the one to make the choice whether or not to do it. The only exception, which I have already stated, is if someone has already done harm to others and we are imposing consequences as an alternative to whatever the natural consequences of what they did would be (for example, trying someone for murder and imprisoning them if convicted, instead of letting the victim's family and friends take private vengeance). I'll assume we are not talking about a case where that exception applies in the rest of this post.

(Technically, there is a second exception, cases like the EMT resuscitating a person, since the person is incapable of giving consent. But I've already addressed that: there is a default presumption that the person would consent to being resuscitated if they could. And note that in our current legal system, a person can override that presumption by, for example, having a do not resuscitate order on file with their doctor.)

In the brain cancer example, I suspect you are imagining a case where you have some treatment that can be done easily from a distance without my perceiving it and without any side effects--it just makes the cancer vanish and leaves everything else the same. I have commented elsewhere in this discussion that I don't think such a thing is a real possibility; there's no way you could ever know that there are no side effects with such certainty. (And if you don't, if you're only 90 percent sure that there will be no side effects, then my rule above applies and you should let me make the choice since I'm the one that will suffer the side effects.) But let's assume for the sake of argument that you are certain there will be no side effects; let's say you have a mountain of evidence from past usages of the treatment, easily available and easily understandable by anyone.

But if that's the case, you have no need to do the treatment without my consent; you could just, you know, get my consent. After all, the treatment is a slam dunk from what you're saying; you have this mountain of easily understandable evidence that says it works great and has no side effects. So why not just show me the evidence? After I've seen it I have no reason not to consent, so I'd just consent. And then you wouldn't even have to worry about making a judgment and possibly being wrong. You wouldn't be making the judgment at all; I would.

In other words, your rule, which appears to be something like "if you're at least 90 percent sure that it will lead to a better outcome, you can do things to other people without their consent", requires you to make a judgment whose consequences you won't have to live with, someone else will, and all history shows that that is a very bad idea. What gives you the right to judge on my behalf that, say, 90 percent odds of curing my brain cancer is good enough? That's a judgment for me to make, not you, because I'm the one who has to live with the results. And in the truly slam dunk cases where the results are certain to be good ones, getting consent is also a slam dunk, so "always get consent" still covers those cases.

In short, "always get consent" (in cases where the exception I gave above doesn't apply) is a simpler rule that leads to better results than yours--it does the same thing in the easy cases, and puts the judgment in the hard cases where it belongs, with the person who will have to suffer the consequences of the judgment.