Merit goods and demerit goods...what's the difference?

A merit good, which will be underprovided and thus underconsumed if the market is left to it's own devices, are goods or services that governments believe are important for society and include sports centers, public schools, and (public) healthcare. Merit goods cause positive externalities, and governments intervene by providing the g/s themselves or by subsidizing private firms for provision. Of course, when governments spend money, the issue of opportunity cost comes into play and an evaluative discussion can occur.

A demerit good, which will be overprovided and thus overconsumed if the market is left to it's own devices, are goods or services that governments believe are harmful for society and include illicit drugs, cigarettes and alcohol. Demerit goods cause negative externalities, and governments intervene by restricting the g/s through taxation or negative ad campaigns or by subsidizing programs aimed at reducing/eliminating consumption. Again, when governments spend money, the issue of opportunity cost comes into play and an evaluative discussion can occur.