> defense of the rich against the poor

Taking this a step further, it's logical to conclude that society itself is a constant war between rich people, who use their wealth (influence/power) to enlist the poor in their attacks on one another. Taking it another level, we could say that "society" itself is merely a side-effect of this war, in fact it is the current state-of-the-art weapon in this struggle. If something better than capitalistic society comes about (such as, most obviously, human-level AIs and robotics), the rich will not hesitate to abandon the society strategy.