My suspicion of metaphysics in general is largely due to the fact that there are many - primarily amongst religious believers - who will claim that some proposition or other ‘ignores’ the metaphysical; in essence, what they seem to mean is ignoring the supernatural.
I’m aware that philosophical naturalism is itself a metaphysical proposition - that is, a statement about the ultimate nature of reality. I agree that philosophical relativism is not a workable position, any more than moral relativism is so - at some point, there has to be a base line by which every other proposition is judged.
However, if we take that base line to be very general - let’s say, the idea that the whole of reality is of one nature and not another, even if we don’t yet know enough to establish precisely what that nature is - then we may have a useful starting point for discussion. My position in this regard is that we have yet to encounter any unequivocal evidence of the supernatural, therefore the working assumption (not a conclusion) is that reality is natural, physical - that all that exists is in principle susceptible to investigation and explanation in physical terms. That is the working assumption behind the methodological naturalism of science.
In light of this assumption, there is ample evidence to support the notion that physical determinism is the case. The arguments against it come (largely) from what we might call the ‘other’ metaphysical camp, the one that considers reality to inhabit two separate realms - the natural and the supernatural. It may well be the case - and there is also evidence for this - that there is randomness within nature, that is, events that simply happen, without any dependence upon prior physical conditions. Radioactive decay seems to be one of these events. Bet that as it may, as Sam Harris (amongst others) has argued, doesn’t give us anything like the classical notion of libertarian free will, since we cannot claim any control over genuinely random events.
There’s much more to be said here, of course, but I’ll go back and read a few more posts before I jump in again…