Even if that is true, in some areas companies' interests strongly misalign with that of citizens. An insurance company earns more by rejecting customer declarations. An ISP earns more by giving customers less bandwidth for a higher price. A toll road company earns more by doing as little maintenance they can get away with, while keeping prices high.

Yes, in a perfect market, customers will flock to competitors that are better for them. However, in many cases a perfect market is not attainable for various reasons. E.g. because the cost of entry is too high (e.g. making a competing ISP would require you to put your own fiber in the ground) or because there are network effects that are nearly impossible to break.

This is why certain markets need strong regulation or government monopolies -- to protect people from pure profit seeking. Health care is a good example. Health care in Western Europe is much better, while less money is spent on health care. This is because health care is strongly regulated and insurance companies cannot f*ck over customers. The objective function of maximizing profits becomes a constrained optimization problem, which generally leads to other ways to increase profits, like pressuring pharmaceutical companies to lower prices of medicines.