One possible endpoint to rapacious social Darwinism is the third-world model of the sharply divided social classes, and demagogues exploiting that. It's happened recently in Venezuela and the result is a disaster. Whenever you have a large number of desperately poor and a small number of fabulously wealthy, economic and social marginalization often lead the have-nots to desperate action. Whenever a people loses hope for the future and the belief that they can build a better future for themselves and their heirs, they feel they have nothing to lose by throwing in with "the revolution". So you get the rise of despots like Chavez and Allende and Castro.
The presence of a large, striving, hopeful middle class has always provided the underpinning of political and social stability in this country. It's what my parents taught me: work hard, be honest, pay your bills (yes, taxes included), treat others with respect, get an education if you can, and you'll be okay. By and large, it has worked. When it no longer does, the wheels come off.