Interesting topic. Happy belated birthday to one of my favorite actors who turned 50 the other day. (Not so charming picking your years in an interview. ) Well, what's there to say about alien visitations?
Pros: The good aliens: Higher intelligence, deeper understanding of the Universe, better looking, environmental awareness, holistic worldview, emotional intelligence, psychic, physically superior
Cons: The bad aliens: Exploitation of humanity, animals and the planet, colonization, they use the Earth as a 'party planet' and have no empathy, almost impossible to to distinguish from actual humans, terribly ugly and thick.