He is a pawn in some respects, but he still maintains his freedom of choice. That and he kills a whole lot of stuff. He kills nearly everyone and everything in Nibelheim, burns the place right the hell down, survives being thrown in the core of the Earth, uses projections of his will to infiltrate the core of Shinra's power and kill the president of the company, subsequently impales a twenty-five-foot snake on a tree without skipping a beat, is enough of an asshole to kill Aeris, almost destroys the whole goddamn planet just so he can give humanity the finger, and THEN comes back to life for round two. If he was any more kill-crazy, he'd be Scorpion challenging kittens to Mortal Kombat.