Pride parades are gay halloween. Gays used to have to hide everything about being gay, if someone accused them or reported them they could get committed to insane asylums and "treated" (read: slow tortured) until cured, or go to jail. So now that the bad old days are gone, they pick one day a year and act as gay as humanly possible. Because they know their history, and their forerunners couldn't do it.
It's like if you lived in the desert, at least one day a year would be a water festival.