Those arrested trespassed on federal property. Now you may think the treatment is harsh, and I agree. But they did violate the law via non-speech / non-petitioning activity. To deny that is just retarded.

What you fail to understand is this...

You cannot outlaw the burning of a flag, but you can outlaw the burning of objects of certain sizes in public or without a permit. Now if such a law exists and you burn an American flag during a protest, you can be arrested for violating that law. That the burning had a speech element does not entail it wasn't the burning of an object in violation of law. To put it another way, the law doesn't care if you burned a flag or a cardboard box and it doesn't look into why you did it. Burning is illegal.