As one who favors a high level of formality in schul, especially on Shabbat and Yom Tov, I sympathize with the OP. There should be dress codes, at least informal understandings of what is acceptable. Some formality adds to the dignity of the place and the subject matter at hand. At the same time, better the people come, even if informally attired, than be put off by the formality and not come at all.
