If there are no rich, who builds the factories?

But nobody would do it then. First, you need a concentration of capital to build the factory, this isn't a function of how much the builders are paid, it's a function of the cost of land, the engineering, the materials acquisition. Second, if you can get the same pay for flipping burgers as someone who goes to college for 8-12 years to learn a really complex subject, why would anyone do that? Communism didn't work. History is packed with it's failures and not a single success.