See, this shows that you (nor Heinlein) don't really understand what "liberty" is. Liberty involves constraint on behaviour - liberty involves the necessity of refraining from infringing upon the life, liberty, or property of others. Without that, you really DO have anarchy - and if you've bothered to even read a sentence of John Locke, then you know that anarchy (what the classical liberal theorists called "the state of nature") is the antithesis of liberty. Anarchy is anti-liberty, since NOBODY's freedom is truly safeguarded. Indeed, the classical liberal theorists, from Locke all the way to our Founders, knew that you cannot have liberty unless it is safeguarded by a consensual, commonwealthian government.
In short - "government" itself is not the enemy of liberty, it's the TYPE and SCOPE of government that is - when it is either not representative of the people (i.e. not consensual), or else expands beyonds its rightful scope of protecting the natural rights of all members of the commonwealth (i.e. is not commonwealthian).
Laws against murder are not a hindrance to liberty. Laws upholding contracts are not a hindrance to liberty. Neither are laws against theft, robbery, rape, kidnapping, etc. (i.e. much of our criminal law). Shoot, laws that forbid you to dump motor oil into a stream that runs through your own property, but then goes through a lot of other peoples' properties before finally ending up in the county water supply - that isn't an infringement on liberty, either.
Much of the problem with libertarians is that they want freedom, but without responsibility. Any enforcement of responsibility becomes tyranny to them - which is simply a childish way of looking at it. Libertarians have a singular ability to fail to comprehend the extended ramifications of their own actions, and that so-called "victimless" actions may only seem "victimless" at that particular instant in time, but are not so "victimless" on down the road.
Most of the libertarians I know and have spoken to have no problem with personal responsibility. In fact, most libertarians would do away with welfare programs, government subsidized medical care, etc. because they believe people should face the consequences for their own actions. A lot of conservatives aren't comfortable with holding people to that degree of personal responsibility.
Libertarians have a singular ability to fail to comprehend the extended ramifications of their own actions, and that so-called "victimless" actions may only seem "victimless" at that particular instant in time, but are not so "victimless" on down the road.
It's not so much that libertarians fail to recognize the cumulative or long-term consequences of certain actions (although some do suffer from this blindness), it's just that they don't believe it is prudent to impose criminal sanctions to address these problems.
Just as some libertarians fail to see the long term consequences of certain "victimless" actions, some conservatives fail to see the long-term consequences of empowering the government to interfere with a person's liberty when there is no immediate threat to another person.
Since pretty much everything we do ultimately affects other people in one way or another, empowering the government to restrict liberty based on the consequences "down the road" really empowers the government to regulate everything. Libertarians recognize the need for a more restrictive standard to keep the government's power from extending over every aspect of our life. The (simplified) standard they support is requiring immediate harm or threat of harm before the state can penalize certain behavior.
That's a significant (but not the only reason) libertarians oppose criminalizing so-called "victimless" acts.