Bored, so I'll play Devil's (Christian's? LOL) Advocate.
Reason 1: Free will does not exist.
If God exists, then God has free will, per Swinburne's definition. But it is extremely difficult to say what free will is supposed to be. Indeed, the notion of free will appears to be positively incoherent: An action must be either caused or uncaused, but it is not free if it is caused or if it is not caused. Therefore, neither free will nor God exists.
The non/ existence of free will is not so easily determined. Reality is rarely binary, and the Christian presumption of a supernatural seat of the personality (aka soul) invalidates the assumption of choice being physically caused or not.
Reason 2: Consciousness requires a brain.
Prove it.
Neuroscience is in its infancy, and this statement is mere assumption. Life as we know it may require a brain to support consciousness, or may not. Again, supernaturalism trumps.
If God exists, God is conscious without a body, per Swinburne's definition. But everything conscious that we know of has a brain. It is more reasonable to conclude that consciousness is a process that occurs in brains than to believe that it is a substance in itself which can have an existence independently of the brain. Therefore, God does not exist.
Since when is God life as we know it?
Reason 3: The problem of evil disproves God's existence.
If God exists, he is omnipotent, omniscient, and perfectly moral, per Swinburne's definition. If such a being existed, then evil would not exist. But evil does exist, in overwhelming quantity. Some apologists attempt to get out of this argument by deploying a free will defense, but as we have seen, free will does not exist. Therefore, God does not exist.
It's not that simple. It's never that simple. Theodicy especially is HARD.
The PoE, which theodicy attempts to answer is
1) almost unique to omnimax Gods
2) arguably flawed at its core, seeing as it
a) presumes equal understanding of "evil" between humans and the Divine, and
b) often fails to distinguish wishful thinking from ultimate benefit
Furthermore, you have not in fact shown that free will does not exist.
Reason 4: Occam's Razor "shaves off" the claim that God exists.
Not really. The Razor is a philosophical aesthetic stating that
all else being equal, the simplest answer is preferable. Lacking data (a coherent theory of divine nature and function, for instance), comparison of a/theistic models is impossible. IOW, we don't know enough to say that all else is equal.
Given the lack of objective positive evidence for the existence of God, it is simpler to attribute belief in God to the intellectual vices and emotional needs of the believer than to an actually extant deity. In cases like this, we can safely appeal to Occam's Razor to "shave off" the claim that God exists, just like we do the claim that leprechauns exist. Therefore, in the same sense in which we say leprechauns do not exist, we can reasonably say God does not exist.
Whoa whoa whoa! It is NOT
simpler to "attribute belief in God to the intellectual vices and emotional needs of the believer," it's pure prejudice, and ignores the the actual testimony of many faithful, myself included.