There are typically two schools of thought regarding this, both of which are valid:
1. He who communes with heretics makes himself a heretic, by implicitly wishing them Godspeed in their works. We should retire from the company of heretics and allow ourselves freedom from the corrupting influences of Satan.
2. Those heretics may never hear the truth proclaimed unless we tell them. Thus, we will be salt to the conciliar church, and work for renewal from the inside, whether by keeping our traditionalism quiet and seeking to occupy positions at CCD and RCIA where we will have the oppurtunity to plant the seeds of Tradition; or by simply not abandoning the Novus Ordo PEOPLE, although we may despise their "priests" and masses.
I have been invited by conciliar priests to teach CCD before. It boggles my mind what I would do...Probably give them all copies of the Douay Catechism and Go line by line...
My Point is that there have been saints on both sides of the fence; I.E. the Great Western Schism, especialyl St. Vincent Ferrer, who defended the Anti-Pope Benedict XIII and was arguably one of the greatest saints who ever lived.
I like the idea of Not communing with heretics. But I also like the idea of not abandoning these people to their ignorance, and if there is something I can do and say, or even if there is a position I could take that could help save souls...
What do you think?