Bear with me on this; I just thought of all this today, so it might be full of flaws; please point them all out and castigate me for being an idiot.
Imagine a world where we do not have free will. Our decisions and actions aren’t guided by our soul, or some other agent, but entirely by our experiences and outside factors. For example, say someone points a gun at someone I hold dear and tells me to give them all my money. In a world where I do not have free will, I don’t have a choice; my decision will be affected by my love for the person, my fear of them or I being shot, my selfishness, etc. And in turn, all these factors are created by causal factors; I may love this person because I grew up with them; I could be selfish because of some event in my youth. All of these factors will add up to my action; i’d hand over the cash. If there were an infinite amount of parallel universes, all the same, where I faced that decision, i’d make exactly the same choice; and it’s no choice at all really, since (thanks to the factors affecting me) I must make that choice.
So imagine that same situation, but in a world where we do have free will. Now there are still all those factors as a part of me, but I have an genuine choice; I can choose to not hand over the money. Of course, being me, I would choose to fork over the cash to save my loved one.
But would I? I have free will, which means I’m able to make the choice and am not dictated to by affecting factors. But if i’m not affected by those factors, what makes me choose to save my friend? Because I like them? Nope, because I have free will - i’m free to go act against that factor. As a person with free will, I cannot choose what I want because I do not want anything; i’m free of all those affecting factors. If i’m not free of them all, I don’t have free will.
So in a world where I have free will, I’m perfectly able to choose to just walk away and leave my friend to be killed. And it gets worse; just because I am not dictated to by affecting factors doesn’t mean I don’t still feel them. So I might choose to walk away even though that makes me feel horrible. And i’m just as likely to make that choice as I am any other possible choice, since outside factors don’t affect me.
I put it to you that a world with free will would be worse than a world without free will.