The Gay-Straight Alliances formed back in the 90s were critical to establishing the LGBT population as a real and recognizable social cohort in need of a distinct codified set of legal rights. Prior to the formation of these groups, it was entirely too common for kids to be taught in school that gay relationships were a sign of physical and sexual abuse, a mental illness, and a moral perversion. Having a community in the school of out-kids who could testify to the contrary made a huge difference in how the subsequent generation of students (and their parents - I got to watch in real time family friends go from implicit bigots to LGBT advocates) perceived of the LGBT population.
Being united doesn’t stop the bullying immediately. But it brings bullying into sharp relief and turns it into a conflict between groups rather than a social stigma against individuals.