I have recently come across Peter Strawson’s argument for soft naturalism in his book Skepticism and Naturalism 1985.
Also as a chapter Skepticism, Naturalism and Transcendental Arguments in Epistemology: an anthology pp.33-41
What strikes me from this is that proponents of hard forms of naturalism are trying to have it both ways, in that they allow naturalism a privileged place where it is not subject to the type of skepticism that the naturalist insists must be applied to all other knowledge claims.
Strawson’s argument for soft naturalism comes out of Hume’s problem of induction and seems a more consistent approach than hard naturalism that is logically unsustainable.