First, none of the anti-war activists I know pose a violent threat, including the one who actually does it for a living.
Second, domestic terrorism has historically come from both the right and the left.
Third, it wasn't all that long ago that the Weathermen and other homegrown American groups on the left were bombing things here - yes, murdering people. Left-wing radicals in the USA have historically become violent just as much than the right-wing ones, quite possibly more.
Yes you must be careful with civil liberties, but you also have to analyze carefully too: Do you have a problem with the feds keeping tabs here and there on the Aryan Nations or Michigan Militia? I sure don't. Why should I apply a different standard here?
Join up, suckas.
"People demand freedom of speech to make up for the freedom of thought which they avoid."
- Soren Kierkegaard