If the Apple's own messages were the same color as SMS or other avenues and Apple made a best faith effort to make sure messages worked, then there would be one less avenue of bullying.

Do you think the bubbles cause bullying?

Yep. Its status and a lot of bullying comes from the world reaffirming your status over others.

I'd imagine the bubbles are just an excuse, which would immediately be replaced with something else in their absence.

Maybe, but it wouldn't be Apple's fault.