And life is too comfortable here for leftists to seriously pick up arms or do anything more than organizing book clubs and mutual aid. I'll take it over nothing but let's not fool ourselves.

state hasn't been murdering and imprisoning right wingers en masse for the best part of a century

This can't be overstated. Compare the treatment of the Black Panther Party to the Sovereign Citizen movement. The BPP created lunch programs, healthcare clinics, tutoring centers, etc. and yet they were completely vilified by the media as a gang of black supremacists. The FBI carried out decades-long campaigns of dismembering the organization with a network of informants and multiple attacks (notably the assassination of Fred Hampton).

Meanwhile, Ted Kaczynski (a.k.a. the Unibomber) killed multiple FBI agents. Timothy McVeigh and Terry Nicols carried out the largest domestic terrorist attack ever on US soil by blowing up a government building. All three men were part of the Sovereign Citizen movement. Despite this, sovcits were able to take over a town in Oregon and the Malheur National Wildlife Refuge HQ in 2016.

So you have a group with a history of violence against the federal government who do an armed takeover of an area, who provide zero community assistance or outreach, and yet it took weeks for the feds to do anything serious. When the BPP protested (while armed) against discrimination in Sacramento on May 2nd. 1967, they were arrested and dispersed that same day, despite breaking no laws.

There continues to be targeted attacks against Black Lives Matter leaders (resulting in the deaths of over a dozen local leaders), while sovcits are free to continue planning mass shootings, bombings, and other forms of terrorism. If you're leftwing in the US and try to help your community or ask maybe the government should give you a trial before they execute you, the state will come down on you with every resource available as swiftly as possible. If you're a rightwing, literal terrorist who vocally advocates for the murder of government officials and violence against the state, you get treated like you parked illegally.

The left (the real left) in America can't use violence not because it is unwilling, but because it doesn't have a state apparatus to do so. We have to get a critical mass of people to the point where reactionaries will be unable to simply send in a SWAT team and run a smear campaign on the evening news. A leftwing, American revolution will essentially require entire cities and counties to come under leftwing control before it even thinks about using violence against the state.