> Called an act of terrorism by who? If you're allowing biased sources to decide what's terrorism for you

By the links you posted. But I mean, for example, I'm curious to know why you would consider the beating of a mentally disabled man terrorism. Or the shooting of a private company by someone with a grievance against said company.

> classifying those acts instead as merely "anti-police" and thus not counting them as left-wing terrorism? The study that separated environmental extremism from left-wing extremism?

Why do you want to lump everything together? Anti-police violence isn't necessarily left wing. I know several conservative black men who are anti-police (not to say they are violent). But if you want to play some sort of game with the numbers, then we can lump in religious terrorism and anti-abortion terrorism with right wing terrorism. Personally as far as I'm concerned I don't see much difference between anti-Muslim terrorists and Muslim terrorists and would classify both their views as right-wing. They're cut from the same cloth.

I'll agree 100% that anarchists and antifa are a problem. Although I don't know how anarchists would be considered right or left. Anarchists as I understand are anti-globalists, which would be something the right would be for. They're also anti-capitalist which is something the left would be for. So I don't know if they fit nicely into this right/left dichotomy.

Either way, every single antifa and anarchist could disappear tomorrow and almost no one would notice, and we would still be knee deep in high-profile terrorist activities. The US mail bombings last year paralyzed the nation for a week. Then there was the Squirrel Hill shooting at the same time that killed 11. Now a NZ shooter that kills 50. Each of these actors were clearly radicalized by the alt-right. The bomber frequently posted right-wing memes [1], the Squirrel Hill shooter was on Gab posting his insanity [2], and the NZ shooter conducted his whole attack for the benefit of social media like 8chan and Twitter.

It seems to me then, if we want to stop these kinds of things from happening, we should target the communities and recruitment methods that radicalize individuals to such extremes. A blanket condemnation of "terrorism of all kinds" while one kind specifically is racking up a body count by the dozens seems to miss the point.

> He was part of several online communities

You left out my qualification "same way ISIS and alt-right terrorists are". There's a difference between being a member of a Facebook group that's political, and being part of something like 8chan or gab. I mean, the secretary down the hall is part of the Donald Trump is Not My President Facebook group. She's not exactly becoming radicalized. The Terminate the Republican Party group in your link is quoted "It's terrible what he did," Pearlman said of the gunman. "I — and we as a group — do not condone this at all." That doesn't exactly sound like a radical terrorist recruiting group to me. Contrast this with the shooting in NZ last week and /r/The_Donald and 8chan are calling him a hero.

[1] https://www.miaminewtimes.com/news/cesar-sayocs-social-media...
[2]https://en.wikipedia.org/wiki/Pittsburgh_synagogue_shooting#...