Ray Allen is a big time traitor, bu that is not the reason why he is hated by so many of his teammates on the Celtics.
I believe the reason he is hated so much is because... The 2008 was the first celebrated Big 3 in history. They won a championship in their first season together. They had a legacy to protect. The Big 3 are a Celtic Legend. PP is a Celtic Legend, KG is a Celtic Legend, Ray Allen is a Celtic Legend. They had a legacy 2/3 of that Legend was willing to protect that legacy, 1/3 walked away ensuring that the legacy will forever be dented, not tarnished but dented. The feel good story can never be written because one walked away. The great ending with the band playing was not to be because one legend walked away.
That Danny traded him is not excuse because the Legend of the Big 3 was bigger than Danny, maybe bigger than the Celtics. If Danny had accomplished the trade, he probably becomes the villain. Ray left, so he is the villain.
To add insult to injury Ray leaves for the rival, and anyone that thinks the Heat were not on the level of rivalry with the Lakers do not understand that for these three the Heat was their Lakers. PP did not hate the Lakers, he grew up a Laker fan. The Lakers took one chip away from KG, Miami stopped him from more than one. And even if you think the Lakers were the real rival the heat were led by the very embodiment of the hated Lakers -- Pat Riley. Ray left the Celtics for the Laker, Pat Riley. You think Pat did not like sticking that to the Celtics?
More insult to injury, probably the biggest insult, Ray, the Celtic Legend, wins a championship for the Heat, for the Laker Riley. That is why this one is hard for the 2/3 to forgive.
I bet it would have been easier to let Ray back if he had fallen flat on his face in Miami. They would have let him back and even teased him a little, but how can you let him back and have him back at the party when you know he helped the enemy win what yall played for. What made you legends. You think they want him around to show off his second ring, like 'her Ray can we see your ring'?