I doubt the bullying would be any different if it was a beautiful red (or whatever is considered a pretty chat bubble) instead.
And even if it was a blue bubble, the bullies would find another reason to bully someone.
I get the peer pressure part and sure Apple might be exploiting that in America, but in the past it was clothing brands or whatever it is now. Making the bubbles the same color (or even bringing iMessage over to Android completely) would get rid of a single symptom, not of the root cause.