What is a good thesis statement for an essay on freedom?

Your thesis is really going to be determined by the support in your paper. Will you utilize the words of the Constitution? Are you comparing the freedoms of those in the United States with those in other countries across the globe? Have you been reading things for a class with a central theme examining the role of freedom in people's lives? Without that type of information, it's more difficult to construct a thesis that is geared toward your needs. That said, if you have been assigned a paper with a central idea of "freedom," these are some ideas that may get you started:
Americans enjoy many freedoms that are unrecognized in other parts of the world.
Although Americans enjoy many freedoms, there is still much work to be done toward equality for all people.
Freedom allows people to pursue their passions and to have the potential to live meaningful lives.
The Declaration of Independence guarantees certain freedoms that are (or are not, depending on your point of view) appreciated by many American citizens today.
Freedom is critical in any society.
Complete freedom is an unachievable goal but one worth striving for nonetheless.
People who enjoy particular freedoms should consciously work toward helping other people achieve the same freedoms.
As you can see, each of these theses would build a paper headed in a completely different direction. With that in mind, hopefully this provides at least enough backbone to help you form the basis of your paper. A thesis is the master blueprint that the paper will follow, so having a solid and supportable thesis is crucial to content development.