I wish this forum had a rep system and I had some rep just so I could give it all to the OP
All but the last part is perfect - my opinion doesn't, in fact, differ from yours. Why? Because your post is logic, not opinion
Some people simply cannot have any fun while they perceive a threat (those people who say, "fight or flight? What does that first option stand for?"). Most of us homo sapiens, however, like to get high on this chemical our adrenal glands produce called adrenaline, which puts any other drug to shame. Doubt and challenge are what make life worth living. Those who don't have challenge in their life - either because they're too afraid to enter any situation with serious challenge or because their lifestyle simply precludes challenge (the over-protected, the super-rich who are relegated to figureheads rather than running their family's business themselves, etc) usually substitute for the lack of adrenaline with some other thrilling chemical - caffeine, alky, cocaine, meth, whatever. If you don't believe a game can provide adrenaline, then you haven't played an exciting game :P
Basically the risk is what makes it fun. Its such an over-used statement because it's true and obvious to most everyone. The reward is cheap and worthless when you didn't risk anything to get it - even more so in a mmo world where it IS literally worthless in real world terms.
And you're right, too. Open PVP and looting will make items more valuable - people will be needing to replace what was looted, supply lines will get raided, good resource spots will be fought over and thereby rendered unproductive from time to time, etc and so on. In addition to that it opens up tons of new positions for the players - guards, bounty hunters, law enforcement, thieves, raiders, mercenaries (blue tribes hiring red tribes to take care of blue competition will and rightfully should be a major thing), detectives (with localized cash and even localized items/styles once the game world expands to new servers/areas, this could become a lot more than just greasing the palms of a few red mercs or thugs for hire to find out who gave them their orders - there are all kinds of things beyond that too, like what kind of resources certain tribes use, which could give you hints and clues in detective work involved with blue-on-blue crimes by proxy), etc and so on, lots and lots of things.
I think you'll find that lots of people agree with you, the main differences of opinion will be on how PK should be managed to keep it from becoming rampant while still leaving the players at risk when they are careless and giving people who want to take the risks of PK lifestyle a worthy gameplay experience. I think that just allowing the "dedicated" early adapters to create their towns and societies under the safe zone rules at first will go a long way. Instead of people just being dumped into a pk haven there will be whole systems of governance and protection set up before you're ever truly always at risk. The main people who will disagree with you are those who just ask for what is blatantly convenient to their play style without thinking about how it will affect gameplay and long-term viability. I guess there are some people who genuinely can get satisfaction from rewards without risk, but its far from the norm in a species which automatically receives such potent chemical stimulation for winning out against danger.
Anyway sorry for the wall of text its just nice when you see a non-pvp player who understands that open pvp and pk helps THEM too, if they're smart. The only people it really HURTS in the long run are the macroers (another large source of people complaining about open pvp, those who want to just turn on a bot and have it get them to top level can't do so when any PKer is going to kill them on sight, even if they usually wouldn't bother that person) and the incredibly dumb folks who don't learn from their first few slaughters not to go into the areas where PKs hang out.