Imagine, for the sake of argument, an alternative future history in which the Merseians, having got ahead of us in terms of faster-than-light interstellar travel, have, in the mid-twenty-first century, occupied the Northern Hemisphere of Earth and are committing genocide in the South. Would the entire human race unite against the invaders? Yes?
No? Might some Northern Terrestrials claim that incorporation into a technologically advanced interstellar civilization was the salvation of humanity and deny that the genocide was happening? We do not know any other intelligent species but we do know our own species!
Sf writers can use fictional aliens to comment on humanity and on contemporary issues. One Star Trek episode referred to the Vietnam War. IIRC, an episode of Star Trek: The Next Generation was not shown in Britain because it mentioned the date of the British withdrawal from Norther Ireland. Futuristic sf is relevant.
Controversial almost to the point of civil war? Certainly. Appropriate subject-matter for sf? Definitely. Like Wells' prediction, then denunciation, of the use of aircraft to bomb cities.
There are at least two kinds of aliens in sf:
those that are used as commentaries (see above);
those that are dramatized scientific speculations about extraterrestrial biology.
Needless to say, Poul Anderson gives us both, e.g.,
the Merseian Roidhunate as an approximate analog of the Soviet Union;
Ythrian biology, psychology, sociology and theology.
In the case of the Merseians, it is the Roidhunate, not the entire species, that is hostile, as Anderson brilliantly shows in A Knight Of Ghosts And Shadows.
Can I praise the Technic History highly enough? No.
