Repost: 

Gay Pride consists of a series of floats affirming the celebration of LGBT people by business; financial institutions; government; churches; unions; police; military; schools; entrepreneurs . . . and, of course, LGBT organizations themselves. Several hundred floats make up the largest parades like the one in Toronto. The people who appear on the floats could be LGBT or could be their straight supporters. The "gay paraders" as you call them could be anybody from the Canadian prime minister to TD Bank employees to somebody in a gay chorus. The particular motivation for participating depends on the individual.