compatibilism makes sense if you believe in souls,

Compatibilism is the stance that the will observed in a deterministic system is free. There are many angles to approach it from, but the way that I believe is the easiest to think about it is this: People can only really understand causality as being predictable or random, and randomness seems to be a poor refuge for free choice (as often as some people try to make this so), so one needs to seriously consider the idea that the “free will” that people on that side of the argument are referring to is a completely incoherent idea. It’s not just something that doesn’t exist, but something that could never exist and can only be made legitimate-sounding by mysticizing it. Whatever it is, for choice to meaningfully be choosing, it needs to have order (such as values in the form of preferences), and the extent to which it doesn’t is the extent to which it is not a choice but instead represents a lack of agency.

Simultaneously, the “free will is an illusion” crowd I think are making an inversion of the same mistake by claiming there is no free will because something that cannot exist does not exist. What people are clearly looking for is an explanation of the connection between the experienced phenomenon of willing and causality. There is no need to reference “illusion” to explain a person willing something, the ordered system of the brain doing what it does in response to its environment is just an example of what choice looks like from the outside, which is neither more nor less true than what it looks like from the inside.

People who claim to be materialists but then cite determinism to call choices meaningless are either playing with words or are idealists in disguise. There is no overarching Fate that dictates how things will go independent of the particular material causes, and how you choose is one of those causes! It is not an Uncaused Cause, to use the theological phrase, but it is still a cause just as much as it is the effect of whatever input you received. You aren’t the ultimate inception point of the causal chain (you can’t even imagine what that proposition means), but you aren’t a loose end either. That, too, would be idealist.