Having viewed some of the extreme violence, profanity and sexually explicit action already present in some MA15+ games, one wonders how much further games developers need to go to make their products appealing enough to indulge the fantasies of adult gamers. However, there is no question that there is a very strong market for it, just as there is a market for R18+ and X-rated movies.
Some of us remember a time about 20-30 years ago when most corner video libraries stocked X-rated movies. Porn had in effect become main stream in the age of "permissiveness". These days, we've pulled back somewhat from that position and R18+ movies is as extreme as you can get from most video stores.
However, that's the crux of the matter as far as games publishers, developers, and adult gamers are concerned. If an adult can legally watch, buy and rent an R18+ movie, why can't the same rating be applied to video games?
After all, the argument that if the R18+ classification is enough to protect minors from being damaged by adult movies, it should also be enough to protect them from adult games seems reasonable. Although some parents are probably lax in policing their kids exposure to R18+ movie videos that they've brought home, in general the law seems to work quite well in this regard.