158 It is always perfectly justifiable to distinguish between error as such and the person who falls into error—even in the case of men who err regarding the truth or are led astray as a result of their inadequate knowledge, in matters either of religion or of the highest ethical standards. A man who has fallen into error does not cease to be a man. He never forfeits his personal dignity; and that is something that must always be taken into account. Besides, there exists in man's very nature an undying capacity to break through the barriers of error and seek the road to truth. God, in His great providence, is ever present with His aid. Today, maybe, a man lacks faith and turns aside into error; tomorrow, perhaps, illumined by God's light, he may indeed embrace the truth. Catholics who, in order to achieve some external good, collaborate with unbelievers or with those who through error lack the fullness of faith in Christ, may possibly provide the occasion or even the incentive for their conversion to the truth.
Source: Pacem in Terris (Vatican.va)