I think this is overgeneralized and the effect that people agree on a set of believes/values/rules isn't a good indicator of the presence of free will. There might be other mechanisms involved.
The latter is some sort of humanism, that ultimately resulted in all the things we collectively seem to value about western societies, while the former is more or less responsible for the biggest problems we have.
So even if free will turns out a complete illusion, it would still matter how people treat each other based on that idea. Usually you can amend it to: “Free will is an illusion, at least for those poor idiots who have nobody but themselves to blame for it, which is why it is socially acceptable for me to exploit them”
(This is not aimed at you, it is just a thought that crossed my mind, when I read your comment)
* or do you exploit others with it until you're financially comfortable and morally uncomfortable, at which point you pivot, mea culpa, and educate...