I think that's simple minded, assuming grand conspiracy and collusion when there's a lot of different groups, beliefs and opinions out there. Some of the things you claim are leftist positions are also held on the right or issues of people on the right as well.

Weaken our military. Liberalize drug use. Anything goes immigration policy.

Not in the negative way you framed it("destroy the US") but these three in particular are actually Libertarian positions, and also held by particular Republicans as well.

The idea that liberalizing drug use would be a bad thing is ridiculous, honestly. Drug law has been a massive failure in this country and is actually one of the major factors that are causing this racial strife and anti-police sentiment, where it disproportionately affects minorities.