That’s a bold claim that I don’t believe holds up. Even setting aside specifically illegal business practices (bribery, violence, fraud) - the robber baron industrialists exploited the rules of capitalism to concentrate wealth and enrich themselves on the backs of their workers and society. They got ludicrously rich, and everybody else got... what? Less competition in the oil industry? In that sense they robbed us all.
Even if you believe that capitalism is the right system for the world, you have to see extreme concentration of wealth as a problem. Put simply, what is better for society: 1 billionaire, or 1,000 millionaires? I believe that it’s pretty clearly the latter.