Free will is subtler than most of the suggested points in the post would suggest.
Randomness. If we can act randomly, that hardly proves or even suggests free will. My determinism could be probabilistic, resulting in things like "in this case I will take action A 20% of the time and action B 80% of the time." It is easy enough to implement something like this in simple computer code, although the objection might be made that it is a pseudorandom number generator we use to roll the dice. However, a random number generator based on measuring the voltage to picovolt accuracy across a room temperature resistor can be made, in this case it is the brownian motion of a bunch of electrons interacting with all sorts of other things around the resistor that produces the random number. This is of the same order of "true" randomness as actually rolling a fair dice would be.
Predictability. Even something which is completely deterministic may require a full detail "simulation" to predict fully. I believe this is the point of bringing up the halting problem in other posts. And the predictor would need to simulate a large chunk of the entire universe including all the 10^23! degrees of freedom of whatever random number generator we might be using to generate probabilistic answers.
The feeling that "I" am controlled by forces or consciousnesses outside of "me" wouldn't prove a lack of free will. My "chooser" might not be completely 1:1 and onto with my "consciousness." Then there would be things that surprised "me" and felt out of "my" control even though the locus of agency was completely within me.
For a long time I believed, very strongly, that I had free will. I thought, why would I even discuss the issue with someone who didn't think they had free will, after all, they were just arguing with me because they had to, not out of a choice about belief.
Now I don't think I have free will. Randomness doesn't make free will. Quantum uncertainty isn't a guarantee of free will by any means, just a guarantee of a kind of randomness that might be particularly difficult or even impossible to predict. Our only hope for "free will" is a fleeting one, that there is "physics" of consciousness in which the particles are conscious and the rules of interaction are called will. Turning the magic into physics, and making me wonder why we would call rule-described interactions in this new physical sphere any free-er than are newton's laws of billard balls in the presence of thermal noise.
I would add: I feel much worse since losing my "faith" in free will. And I may even be behaving more poorly. At least my language describing my behavior makes me sound like a worse guy, more amoral, more calculating. Of course it just may be my signalling that has gone downhill. It could be we need free will so that we can signal to the other humans that we are willing to drink the same kool-aid they drink, and important thing to know when taking collective action.
Given the spike in free-will debates on LW recently (blame Scott Aaronson), and the usual potentially answerable meta-question "Why do we think we have free will?", I am intrigued by a sub-question, "what would it feel like to have/not have free will?". The positive version of this question is not very interesting, almost everyone feels they have free will most all the time. The negative version is more interesting and I expect the answers to be more diverse. Here are a few off the top of my head, not necessarily mutually exclusive:
Epistemic:
Psychological:
Physical:
For me personally some of these are close to the feeling of "no free will" than others, but I am not sure if any single one crosses the boundary.
I am sure that there are different takes on the answers and on how to categorize them. I think it would be useful to collect some perspectives and maybe have a poll or several after.