Putting aside the philosophic concerns and the sentiments..

This idea of the legitimacy of conquest by the advanced is at least unintelligent. Say, several civilizations are evolving along, each would assume supperiority over the other in difference times. If one with good potentials for future superiority gets killed off in its early phase by a more advanced one, then the whole group will miss a better future in which the killed-off one would benefit the whole group by its later phase of developement.