That is pretty damn shit imo. I myself have nothing against gays/lesbians, but I can understand why SOME people dont like them. The rest of the homophobes out there cant even give a reason..."oh...err...its just wrong".
Canceling the prom is just way too far, If they were in anyway decent people they should have just organised a meeting with the couple to discuss the situation(eg, you can come but no making out in front of people) even though imo they should be allowed do what they want!
The world will soon overcome racism and sexism as it has slowly been doing do for years! But there will always be someone..