Environmentalist: Pollution from gasoline burned by cars contributes to serious environmental problems. But the cost of these problems is not reflected in gasoline prices, and hence usually does not affect consumers' decisions about how much to drive. Heavier taxes on gasoline, however, would reflect this cost, and as a result consumers would pollute less.
 The cost of pollution from driving should not be reflected in the price of gasoline unless the amount of pollution produced would be reduced as a result most strongly supports the environmentalist's statements.