>>17896794 (OP)
His argument is quite limited by English grammar limitations. In Romance languages (French, Spanish, Italian, etc.) you have the null subject and the Agent complement.
In Romance languages, an action always requires an agent even if you can just omit the subjet in the phrase, the subjet/agent is still there, hidden but implied and necessary for an action.
In English you say: It rains.
In Romance languages you can say: Rains
But the rain in itself is caused by the storm. By pure logic, every action necessarily requires a subject. The subject cannot be the action itself, since, going back to scholastic physics and metaphysics, the action itself is an accident, not a substance.
And for connatural accidents, such as rain for clouds or the action of thinking for man, they necessarily occur and are derived from a subject whose existence entails the accident as a consequence of its essence.
Man is a rational animal, and storm clouds carry rainwater.