A foreigner can see life in a different country more impartially than it's resident. He often looks at it from an outsider's viewpoint, without love and affection cultivated from little up.
An adherent of a different faith can see both the advantages and disadvantages of another religion. He examines all the subtleties without bias, not ignoring the contradictions.

An alien can see every aspect of the terrestrial life most objectively!

Humanoid Opera