Furthermore it can be said without any exaggeration whatsoever, that the majority of Masses celebrated without altar stones, with common vessels, leavened bread, with the introduction of profane words into the very body of the Canon, etc., are sacrilegious, and they prevent faith by diminishing it. The desacralization is such that these Masses can come to lose their supernatural character, “the mystery of faith,” and become no more than acts of natural religion.
Your perplexity takes perhaps the following form: may I assist at a sacrilegious Mass which is nevertheless valid, in the absence of any other, in order to satisfy my Sunday obligation? The answer is simple: these Masses cannot be the object of an obligation; we must moreover apply to them the rules of moral theology and canon law as regards the participation or the attendance at an action which endangers the faith or may be sacrilegious.
The New Mass, even when said with piety and respect for the liturgical rules, is subject to the same reservations since it is impregnated with the spirit of Protestantism. It bears within it a poison harmful to the faith.
Archbishop Marcel Lefebvre, An Open Letter to Confused Catholics.