Of course, other species on our planet have no qualms about such matters. Think about lions, where a new male taking over the pride kills the cubs of his predecessor. We might debate whether it’s ethical to kill individuals of one’s own species for food in extreme circumstances, but Nature doesn’t seem to have a problem with it if it’s advantageous for the survival of the species. (Nature does not seem to care about the individual at all, sorry). I think the same biological laws would apply to aliens as well. A spacefaring extraterrestrial civilization would be expected to reside at the top of their food chain. The more technologically advanced they are, and the more power they have over their fellow species, the more damage they can do (compare a Stone Age axe with today’s nuclear bomb). That should make us cautious if and when we make contact with an advanced alien species. We won’t know ahead of time whether they have overcome a savage past. Humans certainly have not.