There won't be changing anyone's mind on this matter, but think of it this way. If you are swerving all over the road while driving you will get pulled over and probably asked "have you been drinking", if you are walking around the mall in "tactical" clothing and keep looking over your shoulder, you may get stopped and asked "sir may I help you", if you are sitting in a park with no children of your own in very close proximity to children and look strange, you may be approached and asked sir, "how are you today, are you meeting someone here?"
The point of all these situations is, you are doing something out of the ordinary. When you do something out of the ordinary, that is probable cause to investigate. If you see someone walking down your street and you are pretty dang sure they don't live in the neighborhood, you may go to investigate.
Like it or not, open carrying or even concealing a firearm, is not ordinary by most people's standards. Out side of a gun store or range, I've only seen 2-5 people open carry, oddly one was in IN a LONG time ago and while it caught my eye and I asked someone about it, I wasn't uncomfortable, I thought it was cool, but then again I grew up with guns.
So if the officer's attitude was actually as depicted by the OP (I'm not doubting it was), then he acted in an unprofessional manner. Perhaps he's always an ass, perhaps he was having a really bad day and took it out on the OP....But if you engage in any behavior that is not the norm, expect attention. How you deal with it is far more important than why you are being asked. I'm not suggesting that you bow to the "man" but if you react in a professional manner, perhaps that will rub off on the officer and the next time he has a similar encounter he will react differently as well. Most cops are not power hungry asses...there are some but most are not.
The logic from, can I see you permit, to papers please doesn't add up. What if I were walking down the street smoking a joint, how do the cops know that I'm not licensed to smoke it for medical reasons, they don't, that's why I'd be asked....I actually don't smoke weed for either reason so I'm not worried about that one.
Navy, in MN we have very good guns laws (that means carry and open friendly) police abuse here is what I would consider well below the "average." So my opinion with regards to my words posted here are not out of becoming accustom to being abused, but in fact quite the opposite. In general I've had very positive interactions with law enforcement throughout my life. Sure there are have been some encounters where the officer was less than polite, but most of the time very professional. My favorite (or not so favorite), was I got pulled over in IA for speeding, I rolled down my daughters window as well, she had to see the cop, and he eventually gave me a ticket for speeding but threw in some stickers for my daughter. She asked "daddy what should I put them on?" My reply, somewhere you won't lose them, those stickers cost about $50.00 each LMAO....