A common belief among Christians is that you can cleanse the world by going into it and by associating with it, but the fact is that you cannot fail to be defiled yourself. The instruction to the Christian now is to purge himself from every vessel of dishonor, and to follow after righteousness and peace with those that call on the Lord out of a pure heart.
Isolation is wrong; but to separate from what is evil in the Lord's sight is an imperative duty for the Christian-to separate in order to unite, according to God's Word, with those that call on Him with pureness of heart.