The human mind (if you believe Freud, I think he came up with this) is split into three parts: the id, which handles urges such as hunger, sex and generally strives to be happy with no regard to anything else. The superego, which strives for perfection and is concerned about morality and putting others before yourself, so the exact opposite. And finally, the ego. This is you. When the id screams hungry, the ego hunts for food. When the superego begs "save them", the ego is the one who listens. In effect, the ego strives for balance between the other two. In waking life, most are ego dominant: they are able to control their actions. In the dream, for me and for you, the id is dominant. I believe this stems from the fact that the dream world is like your own private universe, where no one can get hurt. Without potential guilt, the superego is content to just watch. This leaves the ego i.e. you, with only one person to please: the id. Think about it. Pleasure, happiness, euphoria, all can be gained without slightly inconveniencing anyone.

This is good and all, but after doing nothing but sex for who knows how long may get dull. Eventually, you will want to try something new. So, what I do is: I deliberately fight the id. I don't manifest it as, say, a demon and get into fisticuffs with it (though that might work). I just fight the impulse to jump into bed with every dream character I see. Each person has their own way of fighting it. I personally work on a project. Currently I'm exploring the dreamviews academy and searching for my dream guide. Don't think for a moment that dream sex is inherently bad. It's just that I would rather be the one doing it, not some perverted monster in the back of my mind.

Finally, sorry is this post seems too long.