1) Not everything will be BoA.
2) Rares will still be good.
3) You can still trade with your friends in the same game.
4) Account selling and botting won't become *that* widely spread.
5) Trading does affect others.
just to go down your list...
1: everything good will be boa. rares that have exceptional stat rolls are also going to be boa, not just legendaries. crafted items with really good rolls? boa. items you put through an enchanter so as to make them viable? boa. if it's something some one some where would consider worth looking at, it is boa. which means it's worthless to everyone if it isn't an upgrade for your specific party at the time of looting.
2: "good" and "good enough to swap out current gear for" are two drastically different things. with boa, the only reason to give a flying **** about "good" gear is if it's better than what we have. if it's on par, it's worthless, due to boa, not even worth picking up in the first place. it is, in essence, an absolute waste of everyones time, since we are being denied the ability to trade/give away, said "good' item.
3: that's great! oh, wait, no, no it's not. 4 players per game, max. oh look, this really cool witch doctor item dropped. but my only friend who plays a witch doctor isn't in this particular game, sucks to be him, see #2, again.
4: no one will ever buy/sell entire accounts purely because of gear. get this through your head already. they will buy it because WW barbs will get nerfed to oblivion and witch doctors will get a massive buff, and rather than waste days leveling a new character up, you can just buy it and jump right into having fun again. that is why accounts are bought/sold in games like diablo. the specific characters gear is just a bonus to playing something that isn't gimped.
(disclaimer: the choice of barb/witch doctor is entirely my own, there is no currently announced nerf/buff for either class at this point in time.)
5: you use pvp as an example, and with the way this game is set up.. it's a pathetic example.
how would you know if the other player traded/bought his gear, compared to you? how will they know if you did or didn't do the same? on that matter, who's to say whether or not you stomp someone in pvp, and they report you for buying/botting the account in order to get the gear needed to beat them? it affects a very small portion of the game, one that at present, does not even exist yet in a realistic fashion, and, more importantly, offers absolutely no reward for your participation anyway. and if previous implementations of various blizzard games have taught us anything... it will not provide any sort of reward remotely related to the core focus of the game itself, anyway, no matter what.