Generally, you discourage them with taxes or other restrictions. Most developed countries have very high taxes, and various legal restrictions, on tobacco, say.

Generally, you discourage them with taxes or other restrictions. Most developed countries have very high taxes, and various legal restrictions, on tobacco, say. Many have high taxes on sugar. There aren't really _that_ many things which fall into the "clearly harmful, but people won't give them up" category; tobacco, alcohol, sugar, maybe meat (this one can be, and has been incessantly, argued both ways to an extent), would be the big ones.