I can see a point to it for certain age groups, since the ability to distinguish between reality and fantasy is not an ability people are born with, it develops later in life. That could be a legitimate problem in some cases I think. On the other hand, I know that past that point, there is also research which suggest that perhaps it acts as a pressure relief, that because humans are inherently lazy (not wasting energy is a crucial step in your species continued existence), reality escapes can satisfy the urges of people who would otherwise have to deal with their desires by breaking the law.
It does seem to roll both ways though. An example in the other direction is that it's been shown that, for males, playing a racing game and then getting in a real car makes you an objectively worse driver, who is now sort of driving like they are still in a racing game.
It's not a clear cut issue.
GTA 5 was enough to make me go back and check exactly what the M rating meant (I was apparently thinking Teen). I'm actually still surprised that a game that glorifies weed (and it totally does) managed to score only an M.