Once again, I have to ask: why are those mutually exclusive?

Summary:

Foster child of the Mattrain – planet of supermen – Duncan returned to Earth, his birthplace, only to meet suspicion, hostility and hatred. Upon arrival, he was engulfed by an angry populace who, fearing that he was a spy, welcomed him with jeers and signs saying, ALIEN GO HOME!

I very much doubt future Earth people used 1960s anti-imperialist protest sign vernacular.