This opens the victim up to intimidation by the perpetrator. Which might also be illegal (for example threatening to hire someone to assault your family members if you don't let the person go), but then that can be waived as well. It allows large criminal organizations to rule through fear.

But in some situations it does seem to be what one would want (for example the under age people arrested for sexting pictures of themselves). However, if we could rely on common sense in these situations, the people would never be arrested in the first place.