Comment by black_puppydog

Not all are, but they can be. There's typically a bias (can't remember the name, but it's a known concept) to not change the legality of past actions. But there have been and could be situations where previously-legal actions were retroactively outlawed and punished. It comes down to a decision per situation: what is a higher good: the individual's ability to rely on my current action to be legal in the future if it is legal now, or rather the ability of society to deter from things even though the laws haven't been updated yet. Prominent examples of this (sorry for the Godwin spin here) are punishments of Nazis post-war, for actions that were technically legal during the Nazi years. The argument being "being able to rely on the law not being applied retroactively is not a higher good that stopping people from doing clearly immoral things."