There are some people who believe the line between fantasy and reality is a tenuous one. Most people, thankfully, understand the difference between daydreaming and plans of action. A person, for example, could imagine robbing a bank, and even be entertained by the excitement and danger of that fantasy. Is this person then unfit to be put in a position of trust regarding other people's money? I think not. While it's true that a person who will actually rob a bank or steal money is likely to think about doing so, there are many more people who may fantasize about it while having no expectation of carrying out any such actions in reality - because they understand the reasons why doing so is wrong.
It is extremely simplistic and short-sighted to attack imagination in the hopes of preventing crime. You may as well choose people at random, because people of all sorts tend to imagine - and enjoy imagining - all sorts of things. A FAR better indicator of future behavior is to examine not a person's thoughts and fantasies, but their past behavior. A man who fantasizes about bank robberies but has never stolen money should, in principle, be far more trust-worthy than someone who does not fantasize about bank robbery but has a long history of not handling other people's money well.
Some people accept this, but for some reason, choose to draw the line at sexual fantasies. They might say, "other kinds of fantasies, including violent fantasies, are just that, but if a person has certain kinds of sexual fantasies, they are dangerous." But sexual fantasies are just like other kinds of fantasies. A person can fantasize about all sorts of sexual scenarios, and it doesn't have any more bearing on what kinds of acts he will commit in reality than his own record of past behavior would suggest. A man who understands the reasons why certain sexual scenarios are not realistic is in a good position to derive entertainment from fantasizing about them, while a different man who does not understand those boundaries will be in more danger of committing certain types of inadvisable acts, whether he devotes any length of time to imagining such acts or not.
And so it is, like with the bank robber, that a man can fantasize - for example - about being a teacher and taking advantage of his position to solicit his students for sexual favors, and doing so does not put him at particular risk of carrying out any such activities in reality. We can go to the movies and glory in the senseless destruction of cars and buildings, and the careless expenditure of human lives, and noone suspects us to be a wannabe serial killer or antisocial terrorist in hiding. Yet revel in the wrong sexual fantasies (usually the ones that are the most exciting), and people get paranoid about potential sexual predators. I get it - sex pushes our buttons in this day and age. But we need to take a step back and look at these issues more rationally. Sex is not a great exception, it's just a part of human life.
Would you like another example? Here's something I've discovered:
It's possible to be turned on by incest fantasies, despite not actually having a sexual attraction to anyone in your immediate family (I say "immediate" because most people have at least one sexy cousin, and that's hardly the same issue). Some people, I have observed, think incest is gross because they feel disgusted thinking of their actual family members in sexual terms. But the great thing about fantasy is that you can imagine having someone you are sexually attracted to in your family, and then go from there (think: family members have special advantages in terms of closeness and intimacy that strangers and often even friends don't get the benefit of).
I'll be straight with you. If I even consider my parents or any of my siblings in sexual terms it totally squicks me out (I love them, but I'm not sexually attracted to them), but that hot imaginary sister with whom I would have had to share a bathroom (or perhaps even a bed)? I doubt I'd have that sort of interest in a real sister, who I grew up with and knew as a person; but purely as a fantasy, the idea of it pushes certain buttons, and I don't see any problem with exploring or indulging that. The important point here is that incest fantasy does not constitute incest, and an indulgence in or encouragement of the former does not, by necessity, imply a similar attitude toward the latter.
Of course, another reason people think incest is gross is because they consider it a perversion of what should be an asexual interpersonal relationship. They believe family members ought, on principle, not to have sexual feelings for one another, and thus the fantasy transgresses the social order. Even the simple idea of it, alone, is enough to introduce cracks in the conservative conceptualization of "family". But this is simply an attempt at thought control ("we must snuff out all impure thoughts!"). Newsflash: people are going to think things that bother you, and 'pervert' (or blaspheme) your own personal sense of values - whether you like it or not.
But here's the rub: you can't prevent people from thinking those thoughts. And more importantly, you shouldn't. They're only thoughts, and society thrives on diversity of opinion. I happen to take comfort in the thought that 'nothing is sacred', because once something becomes sacred, it is unchallengeable. And that is immensely dangerous. We are flawed beings living in an uncertain world where even "almighty" God himself is incapable of making his existence certain, and has to ask us (through the voices of men - don't you find that more than a little bit suspicious?) to rely on blind faith. Skepticism is the highest virtue. And it cannot thrive where speech is regulated.