Free Will is a sign if God's inescapable weakness

[The Grand Nudger]

I'm actually of the opinion that belief in contra-causal free will overall causes more hatred and revenge fuelled violence and killing than the most extreme behavior of all religions combined.

Unless you count the fact that it may have itself came from religion. I think it might not have done though,  actually I think in all likelihood it predates religion by a long way. When we don't know the true causes of human behavior and we're aware of our own general abilities it's only natural to assume that we are self-causing agents. It's just a lack of analysis. Another example of our so-called "common sense" failing us.

IDK.  Most of the faiths that predate the abrahamic one express a pronounced sense of fatalism, and at the dawn of the abrahamic faith they don't appear to have believed that they had free will either.  We can;t really know what people thought about the subject before these traditions are written down, but by their earliest writings..if people -did- believe in free will in some prehistoric past they'd since moved away from it and began the theological spiral into nonsense we see today.   

And it may seem benign at first, but it's used to justify not only hatred as a whole but also the most grotesquely barbaric behavior. It also justifies arrogance. When people are full of themselves it's often because they take ultimate credit when no ultimate credit is due. The dunning kruger effect, etc. We credit both ourselves and others far too much, rather than focusing on important things like deterring and mitigating harm.

Here again I think it's more a disparity between systematic ideology and common sense appraisals or even our own experience.  It's not uncommon to hear people exclaim that they (or the other person) just couldn't help themselves.  Or for us to express vast bewilderment at why we would do the ridiculous shit we do.  It very much seems like free will is a tool for codification more than an observation on the state of our decisions...and I think it has an effect in societies or people who've been raised to accept it of granting it more credence than we naturally might. We might have had a less fanciful view of ourselves, at one point..or we may not even have had thoughts about it, it being a non-cognitive.

Long lists of taboos are a more direct approach to mitigating harm than assigning responsibility. We were coming up with taboos long before we thought that everyone was somehow directly responsible for their every freely made choice. It seems as though we weren;t counting on people to freely make the right choice..but to remove them from situations, and remove situations from our societies. Can't do the bad thing if you have no opportunity.