I once heard how a friend of a friend had joined the Purim party in a charedi yeshiva. He wore his normal dati leumi clothes, but nobody there thought he was out of place. On the contrary, they assumed he was a charedi guy dressing up as dati leumi. Because he was in fact really dati leumi, his "costume" was correct in all the little details which are hard for outsiders to get right, and he received many compliments for its realism!
One of the things I like about Purim is the fact that in costume, you can't tell if a person is charedi, dati leumi, or (in many cases) secular. When we meet people, we generally begin by relating to them in certain ways, based on preconceptions we have about their background. These preconceptions may not be negative, but they do tend to limit our interaction to certain predefined patterns. On Purim it is harder to do this. Deprived of the usual procedures for determining who is who, the only option is to treat everyone the same way. Then, either we discover that other people are not as different from us as we assumed, or if real differences in outlook come up, we must tackle them head-on rather than diverting then into an "of course THEY think that way" pigeonhole.
Your Purim costume hides some things about you. But your normal clothes, the "costume" you wear all year long, hide much more. On Purim you take this costume off. Physically, it is replaced by whatever unusual and amusing attire you wear instead. Socially, nothing replaces it, and the opportunity exists for more direct and intimate interaction with all members of the Jewish people.