One way for a naturalist to respond to arguments from, say, morality (such as this argument) is to either deny that our moral perceptions are veridical or to reduce the moral to the non-moral, say to a sentiment.
One should see moves that deny the veridicality of a large class of our perceptions (illusionism), or that reduce apparently objective truths to subjective ones, as epistemically costly. One way to see this is to consider parallel responses that a straw man young earth creationist might make to geological arguments:
- Illusionism: Of course, the earth looks like it's billions of years old, but that appearance is non-veridical, being the result of Satan's work at deceiving us into thinking creationism is false.
- Reduction: If t is more than 10000 years ago, to affirm that a geological state S of affairs occurred at t is just to affirm that right now it looks as if S occurred at t.