Why is free will important to you?

I have pretty much accepted the unpopular idea that free will doesn’t exist. That is, we have a subjective feeling that we’re making our own decisions from moment to moment, but in reality those decisions are produced by physical phenomena that are reacting to stimuli in the outside world.

You might disagree with me. That’s okay. But what I want to ask is not whether free will is a real thing, but why it’s so important to us to believe that it is. Is it because we have this very strong feeling of free will? Or is it because the lack of free will would undermine the justice system somehow? Something else entirely?