P1 is, "If naturalism is true, then chemical actions (which are in themselves non-rational) cause mental states in people such as considering, judging and concluding." Are you saying that "chemical actions cause mental states" is not the claim of naturalism? Then what is the claim of naturalism regarding the cause of mental states?I dispute P1, P1 has not been demonstrated to be true. So if P1 has not been demonstrated to be true, then the whole argument fails.
Or are you -- once again! -- refusing to see the difference between a statement about what naturalism claims to be true, and a statement that naturalism is true? Because if you mean "it has not been demonstrated that chemical reactions cause mental states," that's exactly what you are doing. If P1 had been "chemical reactions cause mental states," then "that has not been demonstrated" would be a reasonable objection. But that's not what P1 says. What P1 says is "If naturalism is true, then chemical reactions cause mental states." That's a true statement, even if naturalism is not true, and chemical reactions do not cause mental states!
"If flat earthers are right, then if you travel far enough in any direction, you will eventually come to the great ice wall." This is a true statement, even though such an ice wall has not, of course, been demonstrated to exist. It's a true statement of what flat earthers believe. The same principle applies to my P1.