Cleansing the Temple is a way to take direct and personal responsibility for the condition of the Temple. Finally, driving out the sexually immoral persons from the Church raises moral standards in society as a whole. The record of God's covenant people suggests that we continually live in relationship with those outside the covenant community, whether it is Israel and the Nations or the Church in the World. Paul was extremely conscious of this relationship in recommending action to the Corinthian church. He seems scandalized by the sinful man's behavior, saying it was wrong even by the world's standards.
People watch what the Christian and religious person does.
The Church has long been a moral barometer in Western civilization. In fact, social activists count on this fact when they try to commandeer the Church and religious people to advance their own secular social agendas. Paul envisions a clear line of distinction between the Church and the World. If someone wants to participate in sexual immorality, there are swingers clubs and gay bars a-plenty in the World. But over the Altar of God are a Cross and a Savior, whose blood cleanses us from all sin, including its power and its presence among us.