Not to mention American capitalists, and of course the immigrants themselves. On net, immigrants actually pay more in taxes than they take in benefits. In part, this is because their home countries pay for their education instead of U.S. taxpayers. In the days before the minimum wage, unions, etc., life was terrible for workers because employers paid them whatever they felt like paying them. But then government became more progressive, and changed the laws.
Life is now better for workers because employers' greed has been tamed.
B. This makes no sense at all. Workers have always earned their marginal productivity. As technology progressed, the marginal productivity of workers increased, and labor demand accordingly went up. The problem of workers in the Third World isn't lack of regulation, but low productivity. Of course, low productivity can be a product of a crummy political system, but you can't solve that problem with labor market regulation.