I am an American citizen so I am a FOREIGNER in every other country. I am not bothered by it. It is a fact.
Now "alien" carries with it a certain "strangeness"..other worldliness. The Bar Scene in Star Wars was replete with ALIEN LIFE FORMS. How else would you refer to them? As "foreigners" or something else?
Why do we differentiate among ourselves? Them and us. Are you a them or an us? We tend to us us not them but in matter of fact the "them" may be far more trustworthy than the "us". It's moot.