Because freedom is not an absolute good, we cannot argue that something must (or must not) be allowed on the basis that this will increase freedom. While freedom can be increased or decreased for specific people (prisoners can be set free, and free people can be locked up), when you are dealing with freedom in the abstract, the only thing you can do is move it around from one place to another.
Of course, this does not prevent us from arguing that some person or people should be free: for example, we can always think of people who have been unjustly imprisoned, and campaigning for their release is a good thing to do. But the campaign is always on the basis that (for example) the legal system has failed and this wrongness in the system should be corrected - you never argue this person should be set free because freedom is good.
The freedom to do what I want always needs to be balanced against the freedom not to experience things I don't want. So, for example, the more free you are to be protected from the risk of injury at work, the less free I am to run my business by prioritizing profit over health and safety. If I am free to pollute the river, you are not free to drink from an unpolluted river. If I am free to say what I want, you are not free from the effects and consequences of my words.
So if we increase the freedom of one kind of person, we will always decrease the freedom of another kind. The big question every society faces is always how we should best balance the different freedoms of people in different situations.
A traditional liberal approach is to say that freedom should only be limited when necessary, but different societies differ in what they consider to be necessary. One starting point is to suggest that we should limit freedom in order to achieve certain specific aims.
- prevent actual harm (murder is illegal)
- prevent a significant risk of harm (you may only drive on one side of the road)
- protect property (stealing is illegal)
- protect the exercise of key freedoms (children cannot be employed, so they are free to attend and fully benefit from school)
- prevent corruption (bribing officials is illegal)
When considering society, you can't usefully talk about freedom purely in the abstract - you need to talk about more specific freedoms: who should be free to do what, and when? Most of us easily say that we believe in free speech, but in practice recognize that our speech needs to be limited in various ways. In order to have a sensible discussion about free speech, we need to be clear what limitations we believe should be in place.
So, for example, I believe you should not be allowed to harm me by your speech, but you should be free to say things I find offensive or insulting, and things I believe to be blasphemous.
I also believe that a healthy society should have clear laws which are enforced, but it should also have values which are commonly accepted but which do not have the force of law. Telling lies, for example, should be contrary to our values, but simple lies should not be punished by the legal system. The use of lies to defraud someone, on the other hand, should be punished by the legal system. Cheating on your partner should be contrary to society's values, but it should not be against the law.
When discussing freedom, we often get confused by these different contexts. I am free to commit murder because I have the ability to perform the deed, but I am not free to do it because the law prohibits and punishes such activity. I am free to walk naked down the High Street because I have the ability and the law does not prohibit it, but I am not free to do it because of the social consequences.
[See also Freedom and The Meaning of Freedom]