Why are some crimes all right to "play", and others not?
I dont have an absolute answer only my own opinion.
Most games having violence and crime as part of their gameplay I m able to classify them in a way that enables me to perform them. Its basically reduced to "overcome opposition" and the "act" of killing isnt perceived as killing but more like "One down, 20.000 to go". When it comes to stealing tho the objective in RL terms would be to aquire possessions that are not yours and you possibly hurting another persons life by doing so I dont see it as such. I rather see an objective which I need to accomplish and the game challenging me with all kinds of obstacles I need to pass. Human opponents really are not needed for this nor are ultra-realistic graphics but I m not gonna lie....I prefer nice looks as well. It probably helps that I m not thinking too hard about what I do.
Same as kids jumping into an ant hill "for fun". They are just playing and dont realize they are destroying an entire eco-system killing innocent beings which happen to be weaker then they are. Explain it to them and most will not do it again.
Same with video games. When I perform violence in video games or commit crimes I
know I m not hurting anybody neither do I cause them real loss and I see actual crimes as obstacles. Its the coping mechanism that enables me to enjoy The Division or a match of my favorite strategy game. I dont play these games because I revel in the imagination of the consequences (suffering and death).
I am simply unable to summon this coping mechanism when it comes to certain topics. Same as I have broken my own bones and know exactly what happens I simply cannot watch when a bone breaks. This applies to pedophelia or torture in general. There is NO scenarios in which I could justify these actions to myself even if its in a game. And if a company would offer me gameplay involving any of these activities as core mechanics (there are "sexual assault" games out there) I would mentally blacklist said company and made sure I d never buy any of the products if not openly badmouthing them. Biology works that way I guess. Killing can be justified in the real world if your own life is at stake. This can involve stepping on others heads and shoulders to safe yourself (panic, stampede) or outright killing somebody else if he directly threatens your own life. These acts are often automatic in nature and not a conscious decision. People going through such things (taking a life in self-defense or survive a stampede) are often traumatized. It doesnt mean that their capability to perform these acts brands them as violent persons.
I cannot say how I would see things if I would be born in china tho. Hentai is an art in itself and accepted by the Asian population and it includes stuff that is considered "perverted" in other countries. Anime girls might look like children but people watching these videos or comics "know" they are not meant to be children. AFAIK Asian culture prefers a small statue as well as small hands and feet. I m not sure how this evolved but other countries see obesity as sexually stimulating.
So if you want to know whats acceptable and whats not in a society you need to look at it all in a segmented way. We are all humans but our upbringing is vastly different resulting in cultural disparities which are often "shocking" to the neighbors.