He stabbed us in the back
Ray didn't stab the Celtics in the back. He left an organization that didn't want him, didn't value him, and didn't have a chance of competing. I don't blame him for leaving an irrelevant team with a pain-in-the-butt fraud point guard to join a contender.
1. No one blames him for leaving.
2. No one blames him for leaving to a contender (and the Celtics weren't an irrelevant team at that time). He's blamed for joining the Heat. Period. ONE TEAM. Same would've happened if he went to the Lakers. But that's it.
3. As much as the Celtics didn't value him, they still were the ones that offered him the most money in the market as far as we've heard (and confirmed).
4. The stab in the back wasn't towards the organization, it was first TO US THE FANS. Business is business, that's the nature of the the league, and the organization and players should be treated as such, but there was a lack of consideration for the fans that supported him while he wore Green that was honestly crap worthy. And tarnishing good memories in the process. And more than that, against his former teammates (KG and Pierce in particular).
5. He was soured because he didn't want to accept a bench role. Guess what, after all his pouting that's all he got from Miami... and at a discount.
You're mischaracterizing the problem Celtics fans, whether justified or not, have with Ray Allen.
It's not about the organization vs. Ray Allen. That was never the issue.
It's about the fans and the community vs. Ray Allen.
He did what he thought was best for him, well good for him. It came with some consequences, particularly from a fan-base and community that really embraced him (yes I know there are a lot of trolls who liked to talk crap about him, which player hasn't?) and helped him win his first Championship.
So right or wrong, justifiable or not, doesn't really come into it. There are actions and consequences, and that's it. He can enjoy his other wins in the process, but to me he's not welcomed.