Yekke, along the lines of what’s been said in some of the recent post, maybe what’s bothering you is the fact that this can cause more damage to Yiddishkeit. It’s kind of like the difference between people being Reform and Conservative vs. being secular. If someone is secular, he simply isn’t keeping the Mitzvos, but he is not denying them and he is not trying to make changes. That is why the Frum people in Israel always fight to prevent a Reform or Conservative presence in Israel.
One is an ideology and one is people having trouble keeping something. The same comparison applies to Burka vs. lack of tznius.
I could see how if the Burka women became more of a force, it could make it very difficult for someone who is involved in kiruv or in defending Orthodoxy to explain to people what tznius is about since all the usual arguments (like the ones given above) wouldn’t be very convincing if that’s not what’s happening. On the other hand, the fact that there are people who have trouble dressing tzniusly doesn’t in any way take away from the messages we are trying to give over.