1. Most importantly, it is not in the Bible. Any imperative in the NT calls for the activity of the will, not its freedom. Philemon 14 in the NASB and ESV are translated using the words "free will," but the context indicates a meaning far from a self-autonomous libertarian freedom.
2. It contradicts scores of Bible verses that talk about God being over the human will [Ex 4.21; Prv 16.33, 21.1; Ac 16.14; Rom 9.16; and others].
3. If I had a free will I would never want to employ it. This is just to say that if man is really sinful, then our will, our emotions, our desires, and our thoughts are all sinful. "Your kingdom come, Your will be done."
4. It is different than moral responsibility.
5. It is a philosophical impossibility. We live in a cause and effect universe. Therefore, when you choose to drink orange juice, it is because you were thirsty. You were thirsty because you ate too many saltines. You ate too many saltines because you were hungry. You ate saltines because that's all that was in your house. And so forth. Also, culture, family, social status, race, age... all of these are what cause us to choose what we choose.
6. If free will exists in a theistic worldview, it can only be possessed by one Being. Principally, this is also what makes truth absolute as well. Free will cannot be innate to more than one being at a time; it is the nature of free will.
7. It is different than eternal accountability.
8. Free will has become the center of the application of evangelical teaching and preaching and this is far from biblical. The cross, the glory of God, the grace of God, hope, peace... these should be held out to souls. People should not be told it is all up to them; eternity hinges on their volition; their choice is all God is waiting on; and other sappy anthropocentric nonsense.
9. It implies an impotence in God, not a tolerance in His love. If man has free will, then God necessarily is impotent to that will and He can only cross His huge fingers and hope that we do what He wants.
10. We are always bound to do what we want to do. We can never do what we don't want to do. In other words, the will is free in the same way that it is bound if you want a real migraine... it always carries through with what it most desires at any given time. Go read Jonathan Edwards on this.