The "Drink milk" campaign in my elementary school would be a good example. You should drink more milk, doesn't mean you should drink less water, or juice or whatever. It just means drink more milk.
>Assuming that you can drink an infinite amount of liquid, yes.
You would also assume that people drink their "max quota" of drinks a day, thus being forced to eliminate something to make room. There's always room for milk my friend.
But in practice "drink more milk" means "drink less soda".