I disagree with that. There is no such thing as absolute freedom. My freedom is being curtailed every day by these things called laws that don't give me the freedom to steal, to kill, to marry several people at once. Gewirth's (implied) definition of freedom is unrealistically simplistic.
You are right in saying that our law system destroys freedom, albeit for the wrong reason. The tax system is a legislated system for depriving people of their right to own property, indeed, the tax system basically boils down to stealing 'for the common good' (whatever that is).
In a free-market based society (which basically holds personal freedom and liberty as it's key ideal), we have naturally enshrined property rights. We can sell the product of our body's work (labour) to other's in mutually beneficial trade. We can own property, and we can decide how we wish to allocate our own resources.
However we have no ability to interact with other people's property (unless they agree to it). Killing someone (against their will) is infringing upon their freedom to live, and is patently unacceptable in such a society.
The key thing to understand is that
freedom is not anarchy. There is an important distinction between 'do whatever you want to' and 'do whatever you want to do with your property'. This is the basis of a free society, and I hope you give this some thought.