Most people who don’t keep kosher did not grow up Frum and can’t be expected to keep kosher unless they are “mekareved” first, since they don’t really understand why they should keep kosher in the first place.
Regarding tznius, we are talking about people who know that they are supposed to keep hilchos tznius, they have been taught it many times, and they do keep the other halachos so it should be expected of them (at least in theory) to keep tznius. Obviously, there must be a reason why they are finding it hard to do so, and I don’t think that intimidation is the answer; I am just pointing out the difference between the two.
Also, as Joseph pointed out, when it comes to tznius, you are being machshil others.
However, that still does not help us figure out how to enforce it. Apparently people are having a hard time keeping it, and one must figure out the best way to get them to do so.
Intimidation is not likely to work.