This is a psychological question, really. I'll explain.
If you believe in fate, that whatever you do was destined to happen, you believe that because you're a follower and easily controlled. You'll notice that all of the followers (even the ones that think their leaders!) believe in fate. Why? Because they are controllable, and they are controlled. Remember Mr. Hitler? What was it that he told all of the Germans? Oh, yeah, that "it's fate". Why? It's the best way to brainwash the masses into following you no matter what. The ones that objected are the ones that were true leaders.
Now, I'll discuss freewill. People that defend freewill are the ones that are leaders. They do what they want, when they want, how they want, and with who they want. They control their lives, as opposed to those that believe in fate, who are controlled by their lives. Those that believe in freewill are the ones that either become everything or nothing.
With that being said, I do believe in freewill. I've never accepted the idea of "fate"--the simple thought that my life is controlled and no matter what I do I can't avoid something that happens to me is bullshit to me.
But, you could look at it yet another way.
Fate and freewill could end up being the same thing. For as you believe that you can do what you want, how do you know that you aren't destined to do that either way? Or the reverse--you think that you're destined to do whatever you're doing...but how do you know you're not subconsciously deciding to do whatever you're doing?
This is just like the chicken and the egg, and [according to some]God vs. Atheism. It's unprovable. To me, there's plenty of proof that God exists, but that's another lecture for another time.