Leibniz: If all is explained by machines/mechanisms, then there is an infinite regress of machines. A machine is a whole whose action is explained by the action of a part, and (given the antecedent) this same part would have to be explained as a machine moved by an action of a part ad infinitum. And so to posit mechanism as an ultimate explanation requires that we deny that an ultimate explanation is possible: a contradictio in adjecto.
This is probably acceptable to everybody upon reflection. Who says that everything as to be mechanical? Still, as soon as we’re all agreed that mechanical interaction cannot be primary, then what sort of action must be primary? Given it is necessary to admit natural actions other than the mechanical, ti becomes difficult to rule out non-mechanical explanations in higher-order phenomena. In fact, “Non-mechanical” is a pure negation, and so does not specify the character of the thing in question. Is it dead or alive? abstract or concrete? Is this a physical or metaphysical question? If it is a “blind force” (a metaphor that gets treated as a fact) then why is it not a chaotic one? If a bunch of blind men drove all our cars we would crash the whole works in a matter of minutes; but this is certainly not what the universe looks like it is doing.