> at least in theory The point that they are making is that this 9/11-inspired law would not have, even in theory if one assumes perfect enforcement, prevented

> at least in theory The point that they are making is that this 9/11-inspired law would not have, even in theory if one assumes perfect enforcement, prevented 9/11. They are saying that they can conceive of gun control laws that would have, in theory if one assumes perfect enforcement, prevented 9/11. Coming up with a specific intention of such is not relevant to their point. I’ll answer your question to hopefully illustrate the point: no guns in US airports. That law, in theory, at least would have had a chance of preventing the attack, which is not something that can be said about this one.