Laws stating that demonstrators from opposite parties must stay X feet apart or be subject to arrest. Laws stating that when a rally is held (i.e. one of those where you have to apply to the city for a permit), counter-demostrators must stay X number of feet away. Etc. The laws vary from one city to another, but the Supreme Court doesn't seem to have a problem with these laws.
There have been a number of lawsuits in which those counter-demonstrators contended that the boundary line compromised their freedom of speech. Free speech doesn't mean the Other Side should be forced to listen to you. When people take legal action along these lines, their goal is almost always the same: to make themselves heard and shut their opponents up.
A great example is that incident where a bunch of anti-war protesters showed up at a funeral for a soldier who died in Iraq a year or so ago. Another group of protesters (those Patriotic Riders or something) showed up and drowned out the first group of protesters. The anti-war protesters tried to sue. Problem is, if you have the right to protest, everybody else has the right to protest you.
We have the right to speak our opinions. We do NOT have the right to shove our opinions down other peoples' throats.
The thing I mentioned earlier about Operation Rescue shows that hecklers of every stripe are treated approximately the same way: if you make a fuss in an inappropriate place, the police do have the power to arrest you. Not for sedition or treason or whatever--you can only be arrested for disturbing the peace.
It is a step towards totalitarianism when only anti-government hecklers are arrested. Hate to let you down, G, but it's not happening here.