As the one who said the above (and this is just observation and my opinion, not some sage insight based on years of education on the subject), I look at it a bit differently.
I live in the woods, and am surrounded with all sorts of wild animals all the time. Birds, deer, coyotes, foxes, squirrels, the occasional moose, the occasional bear, marmots, mice, etc.
Though there are tiny personality differences, all of these critters (on a species by species basis) act pretty much the same. Some birds are braver than others, but they still eat the same seeds or bugs or whatever. Some deer are more nervous, some coyotes are more prone to hanging around humans. But overall, each species acts more or less the same.
And my thinking was that these critters, who, because of what they have to do to survive (act based on their instincts) don't exhibit much variety, if we humans are devoid of free will, there would be no mechanism for us to exhibit such wide variety. We would be stuck on DNA based auto pilot and unable to conjure up such an assortment of responses to the same stimuli. I, for instance, don't jump when someone sneaks up behind me and says boo. I joke that I'm so slow that my brain figures it out before my body can react, but I had a little brother who loved to scare people and i taught myself not to react just to bug the heck out of him, and it still works over half a century later. If I lack free will, I have no idea where my ability to train myself not to react automatically when startled would come from.
I am not denying an any way that we have genetic variations (which appear to me to be much wider than the variations I see in wild animals, but that could be because of inbreeding, breeding outside our group, etc.) not do I deny that we have all sorts of subconscious crap (notice that mine will let me call it crap without responding. Cute.) going on in the background. I just find it difficult to accept that our conscious selves are along for the ride and are unable to influence, consciously, the situations we deal with every day.
To me, it is like the old nature/nurture debate, where each side had its adherents for several decades, then finally people started to agree that both are involved in the development of an individual. I think the no free will/free will argument may well come to a similar conclusion.
I'm not claiming that I am absolutely right. Like I alluded to earlier, if I find out I'm a stupid fuck and it isn't even my fault, I'll be pissed. Or I would be if I were free to be pissed. Which I may not be. Which would explain my calm demeanor at the moment.