someone ought to be permitted on LW to argue, for example, that the law should compel Woman X to have sex in some circumstances.

Yes. Anyone should be permitted to argue anything, so long as there is a (new and reasonable) argument towards a desirable goal (and not, e.g., "that way I'd get more sex" [at the expense of women]). Lacking any such argument though, any idea such as your example should be modded down to the nether hells and torn apart in replies (and I believe would be).

I believe that such treatment, showing rape is very much against the social code, would improve the meme pool more than censoring/prohibiting mention of it - which tends to give rise to theories of secret unvoiced support for politically incorrect opinions.

Of course, if such baseless suggestions were posted more than once or twice, we might ban further pointless discussions because they'd be, well, pointless (as well as rather offtopic).