Unless
They themselves are political or religious zealots
Why is it always assumed that "aliens" will be super moral?
I'd like to imagine a situation where we are visited by the alien equvalent of :
Mongols, Huns or Vandals
Nazis - you aren't Werosocii? (alien for aryan)
Hard core Fascists - we are in charge
Wahhabists -what you don't beleive in OUR god - die then
Aztecs - we need to appease our god - could we have 100,000 people a month?
(place tribal group name into raiding) - We're here for a bit of raiding
Julia Childs - my you look tasty