Reasonable by your standard. As others noted not necessarily reasonable by theirs, especially when you contrast it with other games that remain available. It also flies in the face of research that shows that games probably prevent those fantasies from taking place in the real world which seems preferable.

Are you also in favor of prohibiting most booksellers from selling books which either contain scenes of or are exclusively about rape and/or incest? If not, why not?

In addition:

> (and that should've not been on Steam to begin with)

Where do you believe that they should have been sold? Are you proposing a separate "Steam: After Dark" store that only adult humans are permitted to browse and purchase from?