They can be disclosed in the form of sickness induced by pollution. Moreover, though an individual's "utility" cannot be measured, the utility of not poisoning the environment is obvious. In general, people in business often make messes and don't want to have to clean up after themselves. Boo-hoo. Most of all, they want profits to be privatized (and preferably not be taxed) while as much of their costs as possible are socialized (and paid for by taxes on others). All of that is what 'externalities' is meant to address.