Yes, what GP said is true, at least since the 80s. Before that, too powerful monopolies were considered bad for society; that's why Standard Oil was broken up.

Yes, what GP said is true, at least since the 80s. Before that, too powerful monopolies were considered bad for society; that's why Standard Oil was broken up. However, understanding of US antitrust law underwent a shift in the 80s - now a monopoly has to actively hurt the end consumer for it to be prosecuted under the Sherman antitrust act.