All four articles confirm the same thing. He went up to the VP and said that
Your policies in Iraq are reprehensible
. Because of that he was arrested. He WAS acting different to most others around Cheney who were no doubt smiling away and shaking hands. He disagreed with Cheney on Iraq and said so. If he'd been abusive or threatening or simply wouldn't shut up I would see no problem with him being taken away. But he said a single sentence and walked away. As for being 'argumentative and combative' when the agent questioned him. Well wouldn't you be?
John9001's suggestion that you should only have constructive criticism and put it in writing. Well that's ridiculous. If you can't confront your elected representatives and tell them they are wrong to their face then something is wrong.
As it happens, I think it was the work of an over zealous Secret Service agent who now quite rightly is facing a court case. But stuff like that sets dangerous precedents.