I am in the process of writing some stuff based in a free use universe from the perspective of people who do not wish to take part in all the fuckery. Do you have any tips or key details I should keep in mind?

In my worlds everyone is at least open to taking part, so I have no tips for worlds where there are people who don’t want to take part.

That would seem likely to move it out of freeuse fantasy and into “rape fantasy.” They are not the same genre of smut, so you might not get the audience you’re looking for.