A simple example of policies to address market power is government antitrust policies. As an additional example of externalities, municipal governments enforce building codes and license tradesmen to mitigate the incentive to use cheaper (but more dangerous) construction practices, ensuring that the total cost of new construction includes the (otherwise external) cost of preventing future tragedies. The voters who elect municipal officials presumably feel that they are individually better off if everyone complies with the local codes, even if those codes may increase the cost of construction in their communities.
a simple example of policies to address market power is government antitrust policies as an additional example of externalities municipal governments enforce building codes and license tradesmen to mitigate the incentive to use cheaper (but more dangerous) construction practices ensuring that the total cost of new construction includes the (otherwise external) cost of preventing future tragedies the voters who elect municipal officials presumably feel that they are individually better off if everyone complies with the local codes even if those codes may increase the cost of construction in their communities