If Stack was part of some group that was agitating against taxes, there would be a stronger argument.
From his rant:
"My introduction to the real American nightmare starts back in the early ‘80s. Unfortunately after more than 16 years of school, somewhere along the line I picked up the absurd, pompous notion that I could read and understand plain English.
Some friends introduced me to a group of people who were having ‘tax code’ readings and discussions. In particular, zeroed in on a section relating to the wonderful “exemptions” that make institutions like the vulgar, corrupt Catholic Church so incredibly wealthy.
We carefully studied the law (with the help of some of the “best”, high-paid, experienced tax lawyers in the business), and then began to do exactly what the “big boys” were doing (except that we weren’t steeling from our congregation or lying to the government about our massive profits in the name of God). We took a great deal of care to make it all visible, following all of the rules, exactly the way the law said it was to be done."
And that was just his attempt to claim religious exemption. That doesn't cover his learning to try the whole "file as a corporation" scheme that he only mentions passingly later.
Seriously, guys: read the damned rant-- it's posted all over the web. Read it without the DailyKOS or LGF filters trying to interpret for you. The reason he gives the history is to point out that he's actively done these standard tax protester activities with others in the past, and been burned for it. He did the whole tax protest song-n-dance, got hit with his back taxes as a result, and turned around and blamed the IRS in typical paranoid conspiracy theorist rationale. He uses this paranoid rationale as his argument for doing what he did, and openly states that he hopes to be a martyr for this "cause" and to inspire others to do the same. It's all right there in his rant. Did he plan this out with others or come up with this act inside of a group? No, probably not, though if he did the FBI will likely find out and report otherwise. That doesn't change his clear connection to tax protester groups that he admits himself, nor does it change his stated objective for crashing the plane into the building where the IRS offices were. By the FBI's own definition of terrorism, this qualifies without question.
Tim McVeigh doesn't qualify as a terrorist because two other guys were involved in his plot. McVeigh qualifies as a terrorist because of his connections to anti-government groups (militia or otherwise), and for the reaction he hoped to get from the action (which he
explained himself, though in different ways than Stack).