The moralistic fallacy is the opposite of the naturalistic fallacy. The naturalistic fallacy moves from descriptions of how things are to statements of how things ought to be, the moralistic fallacy does the reverse. The moralistic fallacy moves from statements about how things ought to be to statements about how things are; it assumes that the world is as it should be. This, sadly, is a fallacy; sometimes things aren’t as they ought to be.
Examples
Have you ever crossed a one-way street without looking in both directions? If you have, reasoning that people shouldn’t be driving the wrong way up a one way street so there’s no risk of being run over from that direction, then you’ve committed the moralistic fallacy. Sometimes things aren’t as they ought to be. Sometimes people drive in directions that they shouldn’t. The rules of the road don’t necessarily describe actual driving practices.