We are all one in Christ, and we are called to "get along." While we may disagree with others, if those disagreements aren't about core tenants of Christianity, then we still need to recognize that many of those we disagree with are our brothers. None of us are perfect in what we know, so we need to be gracious. We all can learn something, and we should be open to what others have to say.
Of course, if a core doctrine of Christianity is being maligned, then yes, we need to speak out and mark such doctrines and teachers as false.