A terrorist is not a mass murderer, it is someone who uses terrorism to further their political or ideological beliefs. He's done so with anonymous, with activist groups and on his own.
More to the point of the terrorism watch list, having this guy near an airport (or buying lots of household chemicals) would make me very nervous if I was law enforcement. He's like the poster child for the watch list.
what is "terrorism" in this instance? Would the French revolutionaries of the 1780's be considered terrorists? I'm sure they would have had they lost the revolution. I suppose by your definition George Washington was a terrorist?
Take a step back and try to be a bit more objective and realize that "terrorist" is not a classification, it is a label. And the use of that label is politically motivated.
All kinds of movements can have terrorists. Some are successful. Some aren't. It's one of those things in life where for the most part a successful movement can retroactively be seen as good. That is, if they fail they are typically forever terrorists. And that's necessarily so. So yes had the American revolutionary or French revolutionaries failed they would have been terrorists. No question really. Sometimes things require a revolution to resolve deep societal issues that affect a good majority... Sometimes a few people want a revolution (using terroristic tactics) where most people don't agree with that. This is why two sets of people can see a given act as acceptable and not --and would invert their opinion if done back to them.
More to the point of the terrorism watch list, having this guy near an airport (or buying lots of household chemicals) would make me very nervous if I was law enforcement. He's like the poster child for the watch list.