I don't want to have a mind-killing argument

Then don't just tell us what the moral categories are without explaining how you decided this.

That is precisely the argument (read: flamewar) that I am trying to avoid! The point is I didn't want to get into a detailed discussion of sexual ethics, how wrong rape is, and what constitutes rape. This is something that is emotionally controversial for many people. It's what we might call a "hot-button issue".

While I think physical violence usually adds to the wrongness of a crime, I'd still call blackmail-for-sex wrong

So would I. But there are degrees of wrongness, and in my opinion blackmail-for-sex is, if you'll pardon the expression, less wrong than rape.

Do you see what you did there? You automatically assumed that my moral categories were "Wrong" and "Not Wrong", when I was actually talking about "Wrong", "Very Wrong", "Very Very Wrong", etc.

and I'd still point to the same reason that makes violent rape wrong.

I view "violent rape" as a redundant pleonasm (to coin a self-describing phrase), and think that violence is most of what makes rape wrong. The getting-someone-to-do-something-they-don't-want-to-do aspect is also bad, but it's not 10-years-in-prison bad.

This is provided purely FYI, as a statement of my position; I do not intend it as an invitation to attack and demand that I justify myself further. This is not the right setting for this argument.