There seems to be, in the United States, a general assumption that when something is immoral it should be illegal, and if something is illegal it is therefore immoral. This assumption most often strikes those who argue against state interference, since the accusation is always that those who favor liberty therefore favor immorality. People also conflate opposing a program or strategy with opposing the goal of that program or strategy, because a law has been passed to make it so and that makes it good. Has legal positivism actually taken hold in the United States? Or is it the case that it is a convenient mental shortcut for a population no longer skilled at thinking about issues in depth?
Legal positivism is an enemy of any natural rights basis for formulating law. Under natural rights there are standards that a government must not cross, but under legal positivism there are no such standards since the law itself is the standard. Defenders of the state will try to paint libertarians in a bad light by saying “the laws you object to are legally enacted by the duly elected representatives of the American people and those representatives are elected and re-elected without any real objection from the majority of the American people.” That phrase aptly describes the Fugitive Slave Laws, and those who make that argument should be reminded of that fact.
A stronger case can be made that the average person is not a full legal positivist. To be an actual positivist is to embrace a philosophical system. Most people instead think of themselves as pragmatic while endorsing some of the most non-pragmatic laws and programs. It could be called intellectual laziness, but most people have never bothered to consider matters deeply. People seldom actually consider things to be right or wrong because it is law, but instead take the lesser positivist route and believe that what is right and wrong should be made into law.
It is necessary to disengage morality and legality from each other if liberty is to be achieved. If it is possible to say "that is immoral but should not be illegal" and to have that not sound strange then people are free. That they are so often found together shows the inroads legal positivism has made through a combination of poor education and laziness.