There is one part to that argument, you can't argue against. The human mind becomes desensitized after continuous exposure to stimuli. Even if it is an idea that is being suggested, not just the actual experience.
And yes, games like GTA do indeed have an affect on the mind as well. it's not that you're more likely to do something yourself, it is more that you are more likely to be indifferent to acts of violence and will consider them more natural.
Loli anime doesn't explicitly encourage sexualization of children. What it should do is make the mind more apathetic to it being done.
The problem is that that, which you encounter a lot, or be suggested of a lot, loses its novelty and becomes that much more closer to normal.