Ah, but an agent must come about through law or chance before it can act as a cause. So how high do those turtles stack up?
"Ah, but an agent must come about through law or chance before it can act as a cause."
That is the naturalistic assumption. But it is an assumption, not a conclusion. Agents must follow law, but it is an assumption that agents arise themselves from natural law, and/or that law and chance provide complete descriptions of their behavior.
Let's pretend that this is the case -- that agents are completely defined by natural law. This completely undermines any sort of rational thought, because it means that our thoughts are not controllable, but entirely constrained based upon chance and natural law. If this is the case, then we have no reason to believe our thoughts -- they are merely uncontrollable products of happenstance.