[cperciva]

There's a difference between investigating people based on their political activities and investigating people because their comments indicate a likelihood of criminal activity.

To take an extreme case: If I travel around the US and tell everybody I encounter that I think the White House should be blown up, I think it would be entirely reasonable for the Secret Service to investigate. I might make such proclamations out of abstract personal convictions, or I might make them because I'm the sort of crazy person who would actually try to blow up the White House; the whole point of investigation is to determine which.

[fywacro]

Philosophically, I believe you're correct. But in practice, it's all too easy for a government official to harass political opponents for partisan ends, while steadfastly claiming to be objective and neutral. Barring an outright admission of bias, there's no simple way to prove a political agenda.

As a result, US jurisprudence has grown to recognize the potential for government acts to have "chilling effects" on individual rights, even with no evidence of overt bias. Under this theory, certain civil rights (speech, religion, voting, due process) are so terrifically important that government must err on the side of caution, rather than risk discouraging their exercise.

Of course, as with any civil rights issue, we do consider the severity of circumstances in each case. Unfettered free speech swings a lot of weight, but there are always exceptions. Preventing violent terrorist acts (as in your last example) might justify allowing some chilling effects on speech.

However, the courts have vigorously protected speech advocating NON-violent criminal acts (sit ins, protests, draft-card burning) and changes to current laws (drug prohibition). This category seems to cover both your earlier example (marijuana reform), as well as the original situation (tax reform).

And FWIW, kids: This little back-and-forth is a great example of why arguments by analogy don't work.