Should there be a law against it?
Ain't MY logic. It's the logic of the United States Constitution.
But to answer your posed question as sincerely as possible: you are right, there is NO constitutionally protected right to masturbation.
Should there be a law against it? I would prefer that there not be, but I am only one among many.
COULD there be a law against it. Sure. No problem in principle, but enforcement would be problematic, to say the least.
But enforcement issues have never kept people from passing stupid laws in the past, and I suspect that won't change.
Nah, blindness and hairy palms is punishment enough.