You make a good point, Eldwood. If a particular activity is deemed illegal (whether it is sexual assault, or murder or drug trafficking...) then anything that glorifies it / promotes it should be considered at least morally questionable.
And you are right. There is indeed a fine line between the legal artistic representation of an activity (like violence in movies, comics...) and the illegal incitement (instigation to violence, Incitement to genocide or hate speech, which are considered crimes). Many videogames take advantage of the grey areas in the law. Fine. But from a moral point of view, there isn't a grey area: if a game promotes an activity that in real life is illegal, then that's plainly wrong.
Perhaps many believe that what they see on TV, or the games they play don't affect them at all. But is it maybe possible that there are people (even older than 18) more impressionable that can be shaped in their way of thinking by the violence / abuse that they consume on a regular basis? If that is the case, could it be that some of them would act on those acquired thoughts? To deny that would be like denying the power of advertising.
I believe the question to consider should be: what do we gain vs what do we risk? By assessing the risk we would answer the question: is it worth allowing media to glorify illegal activities? At what cost? What are the potential risks? And how do we benefit from it... what do we get in exchange? Is it really worth it? Well, that's open for debate.