In one sense the "come out from among them and be separate" thing is in play, but "retreat" is a whole 'nother thing. We are in the world to call sinners out of the world and into the kingdom of His dear Son. Coming out from the world and into Him doesn't mean retreat from the culture and find a nice little comfy "safe space" in which to sing Kum-Ba-Yah among ourselves. We are to engage and confront the culture, not remove ourselves from it.