Flatbush, if people are lax about wearing untznius costumes, then its not really the COSTUME thats the issue, just the untznius part.
If a woman is dressed totally tzanuah, and a man is attracted to her, that is the man’s issue. If a woman is dressed untzniusdigly, the issue is still the man’s. The woman is punished for her part of the sin, but it still doesnt excuse the behavior of the man.