Conflict between Freedom and Purpose
Your initial choice for that purpose may be considered free, however your subsequent choices will be restricted by that choice.
I pardon the comic reference but it seems valid in such case. An example would be Batman and Joker. You could say Bruce Wayne freely chose to be Batman, his purpose is to save Gotham and to distinguish himself from criminals, he does not kill. That purpose now restricts his decisions as now he subconsciously is not free to kill others. Meanwhile, when looking at the Joker, who sometimes is seen as a nihilist, he does not care about anything as he has no purpose, he just does things, hence in The Dark Knight he says,” The only sensible way to live is without rules.” And the interrogation scene Batman is constantly tempted to break his one rule, but he does not do so because he has a purpose.
I understand your point that a lack of purpose will give you freedom, but my point is that purpose takes away your freedom. I hope this clarifies, and please keep the discussion going!
:)