Honestly, though I hate the whole "mercenary" attitude a lot of NBA players come in with, it's hard to fault Posey for opting out, especially since everyone involved knew he never intended it to be more than a one year deal.
It's like every other job: sure, factors like the working environment and the surrounding areas influence you, but if someone offers a significant pay bump, most people would take it. It's why I can't fault Scal for taking the Celtics' ridiculous contract offer, and it's why I can't fault Posey here.
Plus, Posey's not some Shawn Marion, "I don't care where I play as long as I get paid a lot and am the #1 guy" clone. I have no doubt that if the offers are close and the choice is between Boston and a bottom-feeder, he'll take Boston. But if, say, the Lakers offered him a 5 year MLE (and I'm not saying they could; I'm just picking an example of a championship-caliber team besides Boston), and we only offered him 5 years at the Non-Bird exception, it's not like I'll call him a traitor for leaving. Sometimes you have to step up and pay the players who are important to you, and I have no doubt Boston's owners will do that within every ounce of their power for Posey