What would you prefer: There is life on other planets, including hostile aliens who in our lifetimes will invade earth and enslave the human race. Or… There is no life anywhere else in this universe, and we are utterly alone.
Perhaps they're just bored and looking for sport, like Predator. An alien species would need to be logical enough to possess the tech required to invade Earth, but beyond that could be guided by alien emotions that would seem as weird to us as laughter or honour would to them.