The stifling small-town world of yesterday, for all of its many faults, had one advantage in that you largely knew "who you were dealing with" and pretenders could be identified. Prejudice against newcomers was both a tragedy and a defense.
Left-wing groups have a dilemma: how to be open to newcomers while not being open to destruction by infiltrators who mean harm. I see it often. Local activist groups become hotbeds of discontent and anger when a deceptive individual begins to spread lies or make people turn against each other. Online peace groups get spammed by exactly the kinds of spam that will turn off the members. Guarding against intentional time-wasters and intentional disruptors is always a challenge. People should be aware of these issues whenever they try to work together with like-minded lefties, so as to not let their work get saboutaged too easily.
But DU, while such a delightful combination of openness and diversity, is thankfully effectively moderated and equipped in a way as to give it an immune system against such attacks. Mods are effective, plus as members we all have our own tools for less overt containment of disruption -- like ignore and hide thread. Tools and systems to help a large group of disparate people focus on their areas of interest. And we all learn better when we are engaged, instead of passive consumers. That's considered inherently dangerous by some, isn't it?
When occasional disruptions or intense conflicts arise, don't sweat it. Instead, just be grateful that such conflicts don't overwhelm the place every single day. DU is still the best source of "interactive news", with its own armies of 'volunteer fact-checkers', educators, support groups, nurturers, and inspirers -- a community.