So it's okay for a person to condition themselves to view children as sexual beings?

All accounts I've read are that some people are just attracted to underage people, the same way I'm attracted to women in their early 20s, or Elton John is attracted to other men. Unfortunately for them there's not really a way for them to act on their desires fully without potentially hurting or harming or exploiting other people. The closest they can come is fantasy and role play with a consenting adult. I don't think fantasising for pleasure is likely to lead to carrying out the act. If anything, it would be isolation from social interaction that would push somebody to do something horrible. When they get off to lolicon or shotacon, it isn't conditioning themselves, they are already like that. All they can do is control their urges to act on desires.

Have you seen Taxi Driver? It's only a film granted, but I think it's a really good at showing why someone might be pushed to do something extreme or rash. The protagonist coems back from war, receives no help in readjusting to normal life, has very few friends, has no avenue to release his sexual frustration, has no way of making a difference in a city he views as corrupted and disgusting. The complete lack of human contact warps his perception of how shit actually works and he has the same vigilante-esque fantasies; but he has no release for them. He plays with guns in his apartment, works out, etc. but he has no release for his fantasies. No batman comics to read, no GTA to play, no real direction in life. I think it's an excellent way of expressing the idea that people do not act out immoral fantasies unless a variety of circumstances align to make them feel as though there is no other way.

I get why you say it's fucked up. It creeps me out a lot but there's no proven link that indulging in fantasies (role play with a consenting partner, amassing 6 stars and hundreds of dead bodies in Grand Theft Auto, etc.) definitively leads to people carrying out those fantasies. And given that there's no link, I think allowing someone to vent, indulge in fantasies, etc. is preferable to them bottling up their feelings and desires, growing increasingly isolated and so on until they decide to commit a horrible crime.