A potentially better idea would be to implement profit margin caps for industries with a small amount of competitors. They would become defacto public utilities.
If you cap profit margins, it encourages volume, since the only way to make more money is to increase sales.
Perhaps it could encourage new entrants into the market if a new entrant meant that the entire industry's profit margins were uncapped.
It's pretty easy to create the illusion of no profit though. Look at Hollywood accounting for example. Or how multinationals happen to make no profit in high tax countries. The general technique is to split your entity into multiple parts - the one whose profit is to be minimised pays arbitrary fees to the other, which is in a different jurisdiction.
If you cap profit margins, it encourages volume, since the only way to make more money is to increase sales.
Perhaps it could encourage new entrants into the market if a new entrant meant that the entire industry's profit margins were uncapped.