Salaam.
Rgarding your post, there are two points to be noted:
(1) They consider the cultural side of dress as part of Deen. This is Shirk.
(2) If we go by the dictum: "While in Rome, do as the Romans do", then, what follows is: "While in the Mosque, do as the Musllees do."
What I mean is:
Giving due consideration to other people's sensitivities regarding our appearance etc; to a reasonable extent, is quite in order.
Regards,
A. Ismail Sait.