I haven't read much Kant, but I see where this argument is coming from. I'm not quite sure these actions meet the standard of the categorical imperative, though. I thought it was that a principle applied universally that had negative consequences was wrong.
Hm, this is an interesting point. Mage, too, seems to think that maybe I've misapplied the categorical imperative here. I'm also beginning to think I may have done so. But one second on that.
How the heck do you apply an action universally? Everyone does it? Everyone does it as often as possible?
The standard for a categorical imperative is still going to be circumstantial. That is, an action can only be performed under certain circumstances. So, breaking a promise, for example, could only happen once a promise is made. But then we run into something like charitable giving, where it's an action that could be done indefinitely (or until you run out of money). The trick here is to identify when such-and-such is a duty or obligation to perform. Then, and only then, does it become an action worthy of moral praise. And of course failing to fulfill said duty is immoral.
But my argument may fail because of the principle in play here. At first I thought about this with the following two principles:
1) A person can have sex only with someone of the opposite sex.
2) A person can have sex only with someone of the same sex.
The consequence I argued for would clearly only obtain when we endorse (2). I saw this as clear motivation that we would be duty-bound to accept (1). This would not imply that we should have sex as often as we can with someone of the opposite sex, only that when we had sex (an otherwise amoral act, barring certain conditions) we should endorse principle (1).
But I completely failed to acknowledge the following:
3) A person can have sex with whomever they choose.
Endorsing this principle does get the cataclysmic outcome I had argued for and it still allows for same-sex relations. Especially when we consider that a) the vast majority people are straight, and b) the vast majority of people enjoy having sex.
And, since it's an action that we enjoy, duty does not enter into the equation. Thus sex, in any form, becomes amoral (barring certain prevailing conditions).
This, of course, is much more in line with my actual thinking. But that was fun while it lasted.