No matter to what level a civilization developed, as long as the intelligent creatures that constituted the main body of the society possessed feeling, and that there was a class division in the structure of said society, then desire and selfishness would inevitably exist. There was no exception to the Atlanteans as well.
As the advanced fleet that was sent out by a higher civilization, that mastered the light and heat profundity and had a force that spread over 31 planets, to traverse across the galaxy to Earth that had a relatively lower civilization to carry out a mission and take preventive measures of maintaining the galaxy's purity, in the long interstellar journey — heck, even when they had first arrived on Earth — most of the members would be affected by the feeling of lofty sacrifice born in their hearts out of nowhere.