"You can't put a price on human life" is one common occurrence of this. I thought it was just a throwaway phrase, or a wish of how things could be, but I've regularly run into people who don't understand why we would ever fail to spend absurdly large amounts of money to save a single life.
I have had people say "Is the only reason we aren't doing something about X money" for various forms of X. I personally spent over an hour walking one such person through the concept of opportunity costs, the fact that money is representative of value, &c. with the conversation ending with them still certain that the US Government could just print a trillion dollars and solve the problem.
I have talked to people who honestly think that every person with depression should be forcibly committed to prevent them from committing suicide and respond to the "but only a fraction of those people have suicidal ideation, and only a fraction of those commit suicide" with a "if it saves just one life, it's worth it!" So forcibly committing 8% of the adult population is not too high a cost in their minds.