The entire problem with the shul kiddeishim that spiral out of control is that people forget the very reason why they went to shul in the first place!
I have been in different communities where the physical tznuis was arguably worse than the worst Flatbush kehillah (hate to stereotype, but let’s face it, Flatbush as a majority is pretty pathetic in this regard), but they were always aware of WHY they came to shul and nothing spiraled out of control; on the contrary, there was a decent sense of respectful decorum.
Ay, now you wonder how it could be possible that women could be dressed terribly and not to have mechitzah, but yet comingling and kalos rosh to be rather non-existant?
The answer is thus:
Every human being is on a different level. Some people are going up. Some people are going down.
If you are not going up, the only alternative is down.
In Yiddishkeit, there is no such thing as being stagnant.
So, the bottom line is that the reason for the pritzus you saw, had little to do with the actual tznuis, but rather to do with the downward spiritual path of the people attending. Lack of tznuis, both in dress and action, is only a siman that someone’s spiritual world is out of whack.
So at the end of the day, the question is, do you really want to attend a shul with such people? (or did you only stop by as an obligation?)
They may be wonderful people, and even have moments of growth- but the downward surge can take you along with it.
Please consider carefully, and perhaps ask your own Rav before attending such events.