LMA: I think you are missing a mojar point about R. Hirsh with respect to “seperation.” R. Hirsch was a proponent of separation from non-Torah observant Jewish institutions/organizations. He was NOT a supporter of separation from non-observant Jews as individuals, and he was also not a supporter of separation from non-Jews or non-Jewish institutions. In fact, he saw separation from the non-Jewish world as a perversion of a proper Torah approach and a product of the Ghetto of the Middle Ages.
R. Hirsch distinguished between things NON-Jewish, and things UN-Jewish. Non-Jews should be engaged and interacted with in order to fulfill our mission as an Or Lagoyim. Similarly, non-“frum” Jews should also be engaged and interacted with on an individual level to encourage Torah observance among our own people so that we may be a united Or Lagoyim projecting a single Torah-true vision to the rest of the world. Un-Jewish institutions (i.e., organizations, schools, shuls, ect. run by Jews who reject Torah observance) must be avoided – not because they may influence us, but because our associating with them gives an apperance of legitimacy to their non-Torah outlook.