Because the actions necessary to criminalize it are more evil. It would make people afraid to say anything potentially controversial for fear of being thrown in prison. A decent portion of the posts on FR regarding our favorite religion of peace would qualify as racism in the minds of some.
Exactly...this is the prudential argument. Behaviors don't automatically "get a pass" simply because everyone in society believes: I Really Wanna Do It = It's My Right To Do It.
We have lost the idea that a country exists to enhance the good of the whole, not to guarantee the most radical vision of freedom to everyone. If that were the case, why in the world would we form societies in the first place?
People gave up the "state of nature" to form societies for mutual protection, cultural homogeneity and the division of labor. In so doing, the inhabitants of that society agreed to behave according to certain norms to preserve the order. If you want "pure liberty", then go live on a desert island. What libertarians want is the safety, security, and stability of society while also engaging in anti-social behaviors like drug abuse, homosexuality etc. that would get them killed very quickly in the state of nature
How long would a bunch of heroin addicts last out in the wilderness? Not long. Thus you see that they are not "free" or "autonomous" individuals, but members of a society that are acting in a completely anti-social manner and socializing the costs onto people who do not behave in such a manner. If a rich heroin addict blows through his fortune and then ends up, finally, at the county hospital with a severe OD, who do you think is going to pick up the tab for that? People who do not behave in such a manner
People do not exist in a vacuum. There is no isolated sin or blessing.