mw13: I suggest you go ask your Rov if it’s appropriate to give mussar, whether it’s on tznius or anything else, when you know the person won’t listen.
Also, the issue of whose standards of tznius is also a factor, like the wacko Jews wearing their version of a burka.
Also,yours is not a good analogy. A person lacking tznius harms themselves. The Jewish criminal harms others and yiddishkeit in general and making excuses or defending them is insidious.