Depends on your definition of freedom. I am in line with
@JDTAY on this one, freedom is the absence of (coercive) force.
The absence of (coercive) force does not mean that there can be no contracts nor that contracts cannot be enforced. Only that you cannot be forced into a contract.
The GPL is a contract that you enter willingly (or not). By using GPL'ed software you are bound to the rules of the contract and no rights are violated. Don't like it? Then don't use it.
[edit] I am saying that the GPL does not contradict freedom, however one can indeed validly argue if the essentials freedoms in the GPL is the same freedom as stated above (personally, I do not think so), but it is on the same level as public domain (which is also a contract). [/edit]