“No damage must be done to the harmony between faith and life: the unity of the Church is damaged not only by Christians who reject or distort the truths of faith but also by those who disregard the moral obligations to which they are called by the Gospel (cf. 1 Cor 5:9-13). The Apostles decisively rejected any separation between the commitment of the heart and the actions which express or prove it (cf. 1 Jn 2:3-6). And ever since Apostolic times the Church’s Pastors have unambiguously condemned the behaviour of those who fostered division by their teaching or by their actions.” - Pope John Paul II; Veritatis Splendor
“Still it is quite true that there are circumstances under which a Christian is bound openly to express his opinion on religious subjects and matters; and this is the real difficulty, viz. how to do so without display. As a man’s place in society is here or there, so it is more or less his duty to speak his mind freely. We must never countenance sin and error. Now the more obvious and modest way of discountenancing evil is by silence, and by separating from it; for example, we are bound to keep aloof from deliberate and open sinners. St. Paul expressly tells us, ‘not to keep company, if any man that is called a brother (i.e. a Christian) be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one, no not to eat.’ [1 Cor. v. 11.] And St. John gives us the like advice with respect to heretics. ‘If there come any unto you, and bring not this doctrine (i.e. the true doctrine of Christ), receive him not into your house, neither bid him God speed; for he that biddeth him God speed is partaker of his evil deeds.’ [2 John 10, 11.] It is plain that such conduct on our part requires no great display, for it is but conforming to the rules of the Church; though it is often difficult to know on what occasions we ought to adopt it, which is another question.” - John Henry Newman; Parochial and Plain Sermons
Personally, I would disassociate myself from such people but leave open the possibility of evangelization.