A cheap shot against Lewis on free will?

David Lewis thinks that even if determinism holds, we have the ability to act in ways other than what is entailed by the pre-human state of the universe, P, and the laws, L. Were we to have so acted, a "small miracle" would have happened. The actual world's law of nature would no longer have held. Perhaps in that world there wouldn't be enough laws for determinism or there would have been a new law with exception clauses. Here is a cheap shot:

• On this theory, billions and billions of people daily had the ability to to act such that were they to act so, the laws of nature would have been insufficient for determinism or would have had exception clauses. Why did none of them ever exercise that ability?

Is this just a cheap shot? Maybe. The best answer I see to it is:

• Look: this is all hypothetical. We don't actually live in a deterministic world. There will be deterministic worlds with neat exceptionless laws but there will be many more nearby-to-them worlds with many such exceptions. purposes, the world without exceptions. But for the purposes of considering the compatibility of free will with determinism, we posited this unlikely world.

This is a decent answer. But it does suggest that that we would never have reason to think we live in a softly deterministic world with very uniform laws. For near any such world there will be lots of worlds with less uniform laws, worlds that people had the power to actualize simply by acting differently.