These are fantasies, just that. I do not believe that you will, as a result of reading fiction or viewing pictures, become a murdering rapist. People have no control over the hardwiring that results in deviant fantasies. If you have deviant fantasies it is not because you have chosen to have them. They are not your fault!
It is not the possession of violent fantasies that is the identifying factor in murderers or rapists. Rather it is the lack of concern over right and wrong, the lack of any sense of it. All people possess thoughts that if acted upon would turn them into monsters, yet people are not monsters, because their actions are determined by much more than violent thoughts. So too is it the case with fantasies.
We know the difference between fantasy and reality. For us these fantasies can be an exciting dream. We are very much aware however of how different the fantasy would be to the reality. The reality would be no dream, it would be a nightmare.
The guilt caused by the stigma that society places on such fantasies can however have negative consequences. This guilt can easily engender feelings of resentment and anger towards the society that 'forces' the individual to feel this guilt. The resentment and anger could motivate someone to lash out, perhaps by acting out their fantasies so as to spite society.
I trust you to understand the difference between fantasy and reality. If you are the sort of person who cannot make that distinction, you would ultimately wind up in prison regardless of whether or not you possess deviant fantasies.