In the past few weeks there has been a lot of coverage of the cannibal cop in the US. The short summary is this: He planned to torture, kill, and eat several women. He made specific plans to do so and abused his power as a police officer to forward those plans in ways that were illegal. However, he never actually hurt anyone and his legal defence has revolved around the claim that he was merely pursuing a fetish with no intent to follow through. That defence failed so he has been convicted of a number of serious crimes and will be in jail for a damn long time. I certainly don't debate that he should be convicted but his case is a very interesting one in terms of setting policy.
How far, exactly, are we as a society willing to push this? If we push too far we will be jailing half the population for looking up porn with kink equipment, BDSM, or (fake) coercion involved. If we don't push far enough we could end up watching some truly horrible things unfold because we didn't stop them in time. While the cannibal cop and those like him are scary sorts of people I personally am more worried about prosecuting people too much rather than too little. The government resorts to violence to curb lifestyle choices that aren't significantly harmful (protesting, using marijuana, listening to copyrighted music) and that, I think, is the far more serious threat.
A good example of where these sorts of things become really tricky is pedophilia. Obviously the act is heinous and needs severe punishment but prosecuting people for looking up information on their sexual desires is a really awful thing to do. Unlike, for example, rape porn (which I find highly disturbing personally but which can be made without hurting anyone) pedophile porn necessarily causes extreme harm. This is why I think actual child porn should be severely punished while animated child porn should be legal - we should not be the thought police.
When you hand the government the power to lock people up because they look at the wrong information or think the wrong thing you have to be completely certain they will never abuse that power and put other things on the 'wrong list' and I do not have faith in that at all. Until recently that could easily have included gay sex, for example, and we can all agree that we don't want *our* sexual desires criminalized. I just hope that cases like this don't lead governments to conclude that they need to monitor what we do and think more - sensational crimes tend to go that way with people demanding action and government delivering stupid policies in response.