Heterosexism is a term currently being passed around by liberal, intelligentsia wannabes who subscribe to the current "gay agenda", used in an attempt to rhetorically link the plight of those poor "oppressed" homos with the very real and pressing past and current struggles against racism and sexism. People who view the active practice of homosexuality as being morally, religiously, or socially unacceptable are likely to be labeled as heterosexist. This differs from homophobia in that, rather than fearing homosexuality, a 'heterosexist' will simply view heterosexuality as being the social, cultural, moral, and/or religious norm.
"Only heterosexists would protest the hanging of rainbow-colored 'acceptance' flags over dorm entrances."
"That militant femnazi dyke in sociology class accused me of heterosexism today."