One can rationalize it, but the point is that aliens can't be anything but human beings with exaggerated/de-emphasized characteristics. Apologies to Willie Wonka, but "pure imagination" doesn't exist - writers draw on experience to create characters; everything that exists in fiction is ultimately a recombination of what exists, some of it more novel than others.
I remember people talking when I was young about how awesome Larry Niven's aliens were - so I start reading him, and what he invariably does is select one or two human behavioral traits and carry them to one possible logical conclusion. Everything about Puppeteers grows from cowardice, for example. Protectors are aggressively parental and...well, protective (the Niven formula is really something like selecting a single trait and then motivating the character by a presumed-to-be-universal desire to control everything).