https://twitter.com/obruchez/status/451425008863416321
Harris is talking about an "illusion", but also about an "illusion of an illusion". He’s somehow playing with words and, again, he should be more clear about what he means, but he's definitely onto something. You're right: more research is needed (à la Nahmias). But I think we can already draw some conclusions. We already have some data. Probably not rigorous enough, but that's a start.
I’m not sure people are agnostic about free will (libertarian or other), but they're at least agnostic about determinism. That's a huge difference. To understand physical determinism, you probably need to have at least some background in physics. So, if we go back to your "Ignorance doesn’t imply nonexistence" post, the combustion engine in our case is determinism, not free will. According to science, determinism exists, just as combustion engines exist. Free will? Well, it depends on how you define it: libertarian free will doesn't exist; compatibilist free will exists.
But ask "ordinary people" if they think they have free will or not. You will probably get an answer. Ask them if the universe is deterministic. It will be harder to get an answer. But, apparently, according to Nahmias most people don’t believe in determinism.
Anyway, I’m not sure it’s that useful to talk in terms of agnosticism or gnosticism. As you said "ordinary people" "are just ignorant". Or confused. And being confused is not the same as being agnostic. People are confused about God, the universe, and many things. That doesn’t mean they’re agnostic in the religious sense. Again, according to Nahmias, it seems "ordinary people" are sometimes compatibilists and sometimes incompatibilists when it comes to free will. That’s not agnosticism. That’s definitely confusion.
Re. Robert Kane: are we even sure that he’s a libertarian? From the Wikipedia article about him: "Randolph Clarke objects that Kane's depiction of free will is not truly libertarian but rather a form of compatibilism."
Re. "they are just ignorant. That makes it hard to point to anything wrong": I agree. But as I said, we already have some data. We already know that most "ordinary people" are substance dualists (i.e. they believe in the soul). As Paul Thagard writes in his book "The Brain and the Meaning of Life" (that I’m currently reading), human beings are naturally dualists. It’s the "default position". Even for me, as a materialist, I find it hard to conceive that I am the atoms in my brain.
So I think the illusion Harris is talking about is just that: the natural/default position of substance dualism, the feeling that we’re somehow "free" from the law of physics because we’re intuitively not the atoms in our brain/body. Of course, I cannot talk for Harris, but that’s how I understand it. There really is an illusion there, but you could also talk about confusion, if you prefer. The illusion is more about the feeling and the confusion, about the understanding of that phenomenon (materialism vs dualism, determinism, etc.).
Re. Dennett's compatibilism: I’m still not convinced by Dennett. He sounds very intelligent, but also disconnected. Disconnected from the "ordinary people" who tend to be libertarians. Disconnected from the scientists who tend to be hard determinists and think using the term "free will" is not useful/helpful. But even Dennett seems to admit there’s a problem with using the term "free will", so there’s hope after all... :)
https://twitter.com/avernet/status/449386830484361218
https://twitter.com/avernet/status/449386876130967552
https://twitter.com/avernet/status/449386932196229120
https://twitter.com/avernet/status/449386977045917697
https://twitter.com/avernet/status/449387031739654144
https://twitter.com/avernet/status/449387074529943552
https://twitter.com/avernet/status/449387122953183232
https://twitter.com/avernet/status/449387171133140992
https://twitter.com/avernet/status/449387211218100224
https://twitter.com/avernet/status/449387260627009536
"Re. "Ignorance doesn’t imply nonexistence", I tried to write as clearly as I could, but apparently failed to get my point across. So, let's take a step back. I was still trying to understand what the "illusion" is in Harris' piece. http://www.samharris.org/blog/item/the-marionettes-lament I read him argue that free will, as "understood" by ordinary people, is an illusion. However he struggles to define what the illusion is. I think you found why: ordinary people are truly agnostic about free will. Their position on free will is comparable to small children's take on God. (Which can be contrasted to adult's position on God.) That is: they are just ignorant. That makes it hard to point to anything wrong, because there is nothing to point to. Because ignorance cannot imply existence or nonexistence, discussing free will as understood by ordinary people is sterile. There is just not enough material there for us to find something that would qualify as an illusion. Harris set himself up for failure; one can't prove or disprove ordinary people's take on free will. We can only discuss educated takes of free will, such as Robert Kane's libertarianism or Dennett's compatibilism."