I think the only real "fix" to this problem would be to come out with a 2-way game mode. I've found that a lot of this cross GC hate is just grudge cycling caused by 3-way fights. The game mode encourages it. Adders just gets the most of it because of their play style.
In a lot of the matches I've played, I've seen 2 GC's getting into an awesome fight, but just as one is about to start pushing to victory, the 3rd GC shows up and ruins everything. Mael will be fighting it out with Flames, it's getting heated, bodies are hitting the floor, one of the two of us is starting to buckle....and then.... Adders show up and get in the way somehow. Best comparison I can think of is being blue balled because your roommate walked in on you and your girlfriend. NOT COOL. Did you not see the sock on the door??
Adders probably generate the most resentment in this 3 way scenario because they tend to attack the 2nd place GC. Nothing creates hard feelings like kicking the team that's already down, but it's become expected of them because they do it so often. I had a match just last night in which Mael was leading, but without a single command, the entire Flames group moved on Adders because they were closer. When one person asked why we didn't attack Mael, around 10 people instantly responded with some variety of: "because Adders would have backcapped/attacked/sandwiched/pincered us." Normally I would not have sided with them, but Adders had already done it 3 times in that match alone. I got the impression that most of the team was frustrated because they wanted to attack Mael, but knew that they couldn't because of Adders.
It's not really anyone's fault. It's just the game mode. It seems to me that SE should just do away with the 3 way fights and create a 2 way game. That way, there's no hard feelings over getting rear-ended. People can be bitter because they lost, not because they got gang banged.