Steam is absolutely littered with porn games, unless you have filters set up to stop anything adult rated all you need to do is check the new releases feed regularly and you'll see them all the time.
While I find this game distasteful I do not find any logic in banning it, claiming an adult rated game is somehow teaching kids to rape is as ridiculous as claiming GTA teaches kids to steal cars and run over pedestrians. The funny thing is, this isn't the only "porn game" of its type, far from it, it's just one that's garnered some media attention. I doubt there's anything particularly nasty on Steam, but there absolutely is available via other outlets and there's plenty of pornographic material involving some very nasty fetishes. I have an ex that was very much into some more extreme BDSM stuff, something I wasn't made aware of until a few months into the relationship, partly being why she's now my ex as I was pretty sickened by her interests when she introduced me to them. Terms such as "consent non consent" and "knife play" are frankly things that I wish I'd never been introduced to, call me a prude all you want but good lord that was a hard no from me.
Researchers at the Oxford Internet Institute, University of Oxford, have found no relationship between aggressive behaviour in teenagers and the amount of time spent playing violent video games.
www.ox.ac.uk
This is something that gets revisited at least once a decade in some form or another since long before any of us were born.