James Lee was a nutcase, and the fact that he latched onto primarily left-wing causes for his nutcasery is not an indictment of the Left.
Specifically – Lee’s manifesto lists many points of concern, most of which are focused on ecological concerns. But the post itself neatly excises all of those points, and focuses only on the Immigration-related concern. And implies that, because he cares about immigration, he must be a right-wing neocon nutcase.
Various people start pointing out his eco-related demands in the comments, and these comments are all voted down – and the posters are verbally assaulted for spreading James Lee’s message of hate. from an outsider’s perspective, this looks like a bunch of left-wing folks jamming their fingers in their ears and shouting “I Can’t Hear You, I Can’t Hear You” to themselves to drown out the argument from the other side.
It’s wrong when the right does it – I believe the buzzword-of-the-day is “epistemic closure”, and it’s wrong when the left does it as well.
Any position, if advocated with enough demonization of “the other” is going to attract crazies. That doesn’t mean the position is inherently bad. Having said that, we would all benefit from a reduction in demonization on all sides of every argument.