Free Will Theodicy

[Bucky Ball]

Define free will.   In what way is it free?

I'll let someone else give this a try, ... 
these days it's about decision making, and neuro-science's study of when and how decisions are made, and how much of 
a decision is made on unconscious elements and how much is made on conscious elements. There is a great deal of research on the subject. 
What you decide to do right now is probably not "free" as it's based on a person's past history and everything that goes into that. 
But in the sense one can change the supporting habits that determine what one does in a given situation, .. that could be said to be "free" in the sense that 
you can decide to change what your subconscious references by learning and training for when a certain situation arises.

[Anomalocaris]

so in reality will is an perceptual illusion. In principle what we perceive as the working of our will is but an essentially immutable series of causal chains that is exogenous to our mental construct of self. the only thing that gives us room to imagine it is ours and it is free is we lack the ability to predict its outcome with high precision.

[The Grand Nudger]

We're probably better at conditioning each other than we are at conditioning ourselves. In this sense, society is (hilariously) freer than any of us, if the ability to condition a human brain is what the free in free will stands for.

[Bucky Ball]

so in reality will is an perceptual illusion.   In principle what we perceive as the working of our will is but an essentially immutable series of causal chains that is exogenous to our mental construct of self.   the only thing that gives us room to imagine it is ours and it is free is we lack the ability to predict its outcome with high precision.

Agree partially 
For a given moment / decision, what the brain references in making a decision has to already be laid down in it's chemistry. One cannot decide to do something 
one has no prior familiarity with. What is going on may or may not be exogenous to a self image. One could decide to specifically act contrary to it, in certain circumstances. 
Free will is a bad label. I don't think neuro researchers use it any more. It was a long road in getting it established that a substantial amount 
of a decision is subconscious, AND the decision is actually made before we are conscious of it, (by a few seconds).

[Nolin Lane]

When you ask them why would an omnipotent and good God allow evil in the world, the most common response Christians (and I imagine Muslims, but I am not sure about that) give is something along the lines of: "Suffering is a necessary consequence of free will, and it is more important to God to allow free will than to eliminate suffering. All the suffering is ultimately caused by free will.". What do you think, what is the most effective response to that?

I think one of the best responses to that is: "Suffering has existed for hundreds of millions of years before free will, unless you will claim non-human animals have free will and should be held responsible for their actions.". I have started a thread about that on Christianity StackExchange. Honestly, the responses I received there are so ridiculous that I think my time would be better spent elsewhere.

This is not a very complex argument from the Christian perspective. 

I would provide a simple response such as this....what aspect of free will allows an infant to suffer from disease or be sacrificed (which still happens in the world) or suffer in anyway?  What component of free will is an infant not exercising that would prevent them from suffering this way?