> it has no bearing on the subsequent widening of the illegal gun pipeline

All guns were legal at one point. Buy backs, fewer sales etc mean fewer legal and illegal guns in circulation (unless you see an increase in illegal smuggling and manufacturing - but obviously that's a problem you need to address first then). There will always be demand for weapons, legal or illegal. Just like with drugs. If you don't want people to buy illegal drugs or illegal guns, you only need to keep supply so low that prices are too high for most.

The problem for the US is that there are already so many guns, that effective legislation is problematic. For any legislation to be effective you'd first need to lower the amount of guns in society - because as you say otherwise there are too many guns that flow into the "illegal gun pipeline". So it's a chicken and egg problem. The questoin is: is it really an ok solution to say "we can't change regulation to something that would mean less guns in society because we have too many guns"?

> It's interesting to me that a lot progressive, popular armchair analysis of the issue advocates for strict gun laws, and at the same time advocates for loose drug laws

I think progressives mostly argue for looser drug laws for USE, not sale, apart from possibly also legalizing a few drugs. I don't think many progressives argue for lower penalties for drug smuggling, manufacturing and sales. The big difference between gun ownership and drug use in that context is that gun ownership would be a choice. If you are conservative you might argue that using drugs, being gay etc. is also a choice - but that's the philosophical side of it - I won't go there.