I think the reason a lot of people are uncomfortable about sexual arousal may be that we are capable of being turned on by some fairly alarming things sometimes (consider: the appeal of transgression, also the reason people are drawn to or threatened by rebellious music). And these people don't have the confidence or the assurance that if some atrocious idea appeals to their sexual desire, that they will have the power or the will to prevent themselves from pursuing it or engaging in it.
And so sexual desire becomes this frightening, monstrous thing, that resides within our selves and constantly threatens to turn us into monsters. So we shun it, and, likewise, we shun other people who are less restrictive than us about their own sexual desires.
We fear those who freely fantasize, because we see them giving in to their twisted desires, and we think they are becoming monsters, and it scares us. It scares us that they exist, and it scares us that as a society we would consciously allow people to do that. If exploring one's sexual interests beyond the purely mundane is seen to be a path toward chaos, then it cannot be condoned.
But this is all fear of what may be. The BDSM community, in particular - which, you'll notice, has had a history of being acutely feared by the mainstream for some time - is in an excellent position to demonstrate that people can have disturbing sexual desires - like the desire to whip someone, or the desire to be whipped - and they can engage in them humanistically, by communicating with partners, and only engaging in consensual play, so as to create the illusion of whatever degeneracy turns them on, without becoming soulless monsters, hellbent on hurting others and corrupting innocent people for selfish sexual satisfaction.
This needs to be discovered by the mainstream, if we are to continue to pursue the path toward healthy sexual enlightenment. People need to learn that they can explore what turns them on, without it taking control over them. And they need to learn this so that they CAN indulge in the fantasies that turn them on without believing that it justifies their becoming actual monsters. So that, for example, a man can discover that dominating women turns him on, and still be able to understand that it is not okay for him to dominate women outside of a sexual context, or to dominate women who do not consent to be dominated by him.
I tell you, this is imperative to our smooth running as a society, that we confront and address and learn to mend our sexual hang-ups, because the way we are now - frightful of anything remotely sexual because "what if!" is not a healthy way to be. When we turn our heads from the shadows and condemn them to the corners of society, we are indirectly condoning the darkness, even as we preach against it. A new approach is needed, whereby we confront the darkness, accept that it is a part of human existence, and learn how to acknowledge it without letting it control us.