My point being gun ownership requires common sense and responsibility. It's fine to protest government's gun control laws but do it in a way that doesn't make you look crazy.
I also don't understand why it is unpatriotic to co-operate with the police. There is a difference between the police randomly pulling you over so they can search your vehicle for anything illegal and responding to a call to checkout a guy standing on the side of the road with a loaded gun harnessed over his shoulder waving a flag at cars as they pass by. Seems nutty to me.
Would it be okay to confirm that he isn't mentally unbalanced by having a simple friendly conversation with him? Would be okay to ask him to secure his gun so you can approach him to have that conversation?