Trust is hard to earn and very easy to lose. The appropriate answer to somebody violating hard-won international laws and norms isn't to just also start violating them.
Laws are for participants who willingly obey them. If they don't they automatically shouldn't be covered by them. There might be separate subset of laws on how to treat them but they cannot be treated the same as conforming entities.
You have freedom but if you do a crime your right to freedom is void. Now you have right to get punished.
Not sure what to call a rule that immediately stops applying to any involved party as soon as one violates it, but "law" isn't a word that comes to mind.
Our usual understanding of law has an enforcement mechanism of the nation on individuals, not voluntary agreements sovereign nations enforce on each other.
You have freedom but if you do a crime your right to freedom is void. Now you have right to get punished.