Murder, rape and kidnapping are acts which deprive others of liberty.
The matter we're discussing infringes nobody's liberty. It concerns only individual actions and choices which affect only the individual in any potentially adverse way. There is a huge distinction between having laws to prevent/punish murder and having laws to prevent/punish some sexual preference. Murder is absolutely wrong from every perspective (except perhaps a psychopath.) Sexual 'perversions' may be extremely perverse to some but not perverse at all to others, it's subjective. So why do some uptight people get to decide what is or isn't sexually acceptable?
If someone gets to legislate simply based on them finding something immoral or perverse, where do we stop? What if I find it to be immoral to have a bad diet or to not exercise, or to drive a car, etc? Where does it end? Who gets the final say? Where do they derive the right to save someone from themselves, or to be some kind of society architect? If there's anything I know about government, it's that NOBODY is a suitable architect of society.
How about instead of that, we just base our laws on liberty. If an act diminishes the liberty of another, there should be a penalty that mirrors the extent of liberty deprivation. If an act serves only to make someone personally less 'moral,' (in someone's narrow view) how about we not be Nazis about it. We don't need a perfect people, everyone living up to someone's idealized view of morality. We just need free people and the ability to tolerate each other.