When someone has too little freedom, we say that they experience tyranny. Typically, this is where the analysis ends, with the idea that more and more freedom is an unlimited good. I think that this is wrong.
For example, there is a word, which is related to ‘liberty’, that reflects a sense of too much freedom - libertine, as in dissolute or licentious. (The word libertine comes from libertinus, and originally meant a freedman, that is, someone freed from slavery.) Following from this, on first approach we could be tempted to say that high levels of external pressure result in tyranny, but that low levels result in libertinism and we could call that optimal spot in the middle liberty.
Yet, this isn’t quite it. When a person has high levels of personal responsibility, it is natural to think that the optimal state for them is lower levels of external constraint than that of a person with low levels of personal responsibility. As a child grows up, for example, they are accorded more and more freedom, as their personal responsibility increases. It follows that there are two relevant variables in determining whether a person is at the optimal spot - first, the levels of external constraint, second, their levels of personal responsibility. It is in cases where there are low levels of personal responsibility combined with low levels of external constraint that people typically fall into what we call libertinism.
This transfers naturally to political analysis. When a people have low levels of external constraint, and high levels of personal responsibility, we say that they have liberty. However, this is where political analysis usually runs aground - for we say simply that high levels of external constraint result in tyranny. Following from the previous analysis, this isn’t quite right. If people have low levels of personal responsibility, high levels of external constraint might be optimal for them - and I’ll use the phrase benevolent paternalism to describe this.
We can think of there being quadrants that describe the major possibilities here:
Low external constraint and High personal responsibility = liberty = good
High external constraint and High personal responsibility = tyranny = bad
Low external constraint and Low personal responsibility = libertinism = bad
High external constraint (of a benevolent kind) and Low personal responsibility = benevolent paternalism = good
(There is a fifth important type, High external constraint (of a malevolent kind) and Low personal responsibility = malevolent paternalism = bad.)
The basic idea is that people need some match of external and internal constraints in order to have an optimal situation.
The problem with many libertarians is that these people, themselves, typically are very intelligent and have high levels of personal responsibility. So for them, low levels of external constraint are optimal. What does not follow, however, is that their personal situation applies to most of the rest of society. Yet they argue as if it did. (It is a similar problem with upper-class intellectuals grappling with social problems - they think that people in, say, the lower classes, would respond to a given situation as they - the upper-class intellectuals - would. Yet, this is often not the case.)
When a people have low levels of external constraint and low levels of personal responsibility, society falls into libertinism. Arguably, our society has moved closer to this situation over the past 100 years. This leaves a vacuum for external constraint, and usually what results is some form of tyranny (understood in the general sense, what is called malevolent paternalism above) - although one can hope for some form of benevolent paternalism. The only way out of this, and towards what most people think is truly desirable - that is, liberty defined as low external constraint and high personal responsibility - is to create people with good characters (that is, knowledgeable and virtuous people).