I don’t think the left has unilaterally disarmed. I know plenty of leftists — some of whom are ex-military — who have firearms and know how to use them safely.
And I do *not* agree with harming those we disagree with.
But I see your point that the right seems to be much more organized, and therefore, more effective. Part of it is that we on the left tend to resist the kind of military training and obedience to authority required for this kind of organization. And most of us want to resolve things peacefully, through the proper legal channels — despite all the evidence that that isn’t always possible.
Another factor to consider is that way back when, there were some organized, leftist militant groups like the Weather Underground, AIM, and the Black Panthers. But unlike with right-wing militias and hate groups, the FBI came down *hard* on them (sound familiar?), so the organizational knowledge and leadership was taken out decades ago.
But the time might be upon us to get organized — not to take lives, but to preserve our democracy.