Yes, you're free to protest - legally
But the obnoxious anti-war protesters don't have the right to intentionally block traffic without some kind of "parade permit" from local authorities. Basically, these self-centered jerks don't care what problems they're causing the people who have to use the roads to get places on time.
Why can't these protesters demonstrate and exercise their right to free speech in a more civilized manner, in public squares or on the sidewalk?