“Tznius and kosher are both halachas from Hashem that we are equally obligated to follow our Torah obligations on.”
And this is the message that needs to be taught. A healthy level of yiras shamayim, in my opinion, is how someone will achieve this. Browbeating someone to follow a halacha because lack of observance is a nichshol to others, is a stupid tactic, in my opinion. Then again, my opinion only matters when it comes to my wife and daughter. Someone elses wife and daughter if for him to determine the best course of action.