There are different kind of things one law can forbid - things that are in itself bad. (E.g. killing, stealing, ...) - things that are neutral, but could be u

There are different kind of things one law can forbid - things that are in itself bad. (E.g. killing, stealing, ...) - things that are neutral, but could be used to do other illegal things (encrypted message, selling weapons, ...) The second category of things doesn't need to be illegal since the perpetrators would only be doing something bad if they violate a law for the first category and therefore can be prosecuted for that. But making it illegal prevent the potentially good use of it.