Liturgy in general is ritualized prayer, i.e., the official prayer of a society approved by the authority of that society. In the case of Catholic liturgy, there is the additional fact that it is in some way the prayer of Jesus Christ Himself, the Head of the human race, carried out in union with His mystical members.
As regards the New Mass, the element of approval by authority is certainly present [at least de facto, if not de jure—Ed.] so any doubts regarding its legitimacy must concern something deeper—either some antagonism against the very notion of prayer or some incongruity with its status as the prayer of Christ.
All prayer has a double aspect—a primary, ascending aspect by which the adoration, thanksgiving, petition, and expiation of man is offered to God and a secondary, descending aspect by which the gifts and blessings of God are poured out upon man. Having acknowledged God for Who He is and giving Him the recognition which is unique to Him, Man humbly but confidently expects to receive from God those things which He alone can give.
When one considers the ascending aspect of prayer, one immediately realizes how much it depends upon and corresponds to man's knowledge of God.
In adoring God, man acknowledges the perfections which are known to him through reason and especially by faith—God's mercy, power, justice, wisdom, etc.
In praising God for His perfections as better known to man through faith, man also acknowledges the veracity of God.
In thanking God, man thanks Him for His goodness and mercy insofar as he knows of it through reason and especially through faith.
In petitioning God for blessings, man's confidence is rooted in his knowledge of God's power and mercy.
In seeking God's pardon, man is motivated by his knowledge of the malice of sin, the goodness and majesty of God, and man's own insignificance in comparison with His Creator.
Here lies the first reason for the illegitimacy of the rite of the New Mass—that it does not correspond to man's knowledge of God, i.e., to the truth of God's revelation considered either in its natural mode (via creation) or its supernatural mode (via revelation). The new rite in a certain sense worships a God of its own making—a God not offended by sin, Who is not interested in ritual sacrifice, Who has little respect for His own physical Presence at Mass, and Who places religious truth and religious error on similar footing.
God's real perfections and His real, historical dealings with men which reveal and express those perfections are ignored or re-interpreted according to the preferences of a modern man obsessed with his own dignity rather than the dignity of God. Objectively, such a rite of Mass is an insult to God.
As regards the descending aspect of prayer by which God's blessings are called down upon men, a rite of prayer will be legitimate insofar as it disposes man to receive these blessings. At the level of natural religion, this will require that the rite be so designed as to arouse sentiments of humility, confidence, and contrition. At the level of supernatural religion, the rite should dispose man to acts of faith, hope, and ultimately charity. At this level, the Novus Ordo rite again proves defective because it obscures the truths of the faith—hiding those elements of doctrine which offensive to ecumenism or the modern notion of human dignity. Praying with such a distorted expression of the faith certainly does not facilitate acts of faith but rather impedes them. This undermines the whole structure of supernatural sanctification since faith is the foundation of hope and charity. Even considering natural religion, a rite which places man at the center of religious focus and a man eminent for his intrinsic dignity which no sinful act can compromise can hardly be said to dispose men to acts of humility and contrition. In fact, in practice, it is obvious that the new rite of Mass has undermined the natural religious reverence of the faithful.
Finally, all Catholic liturgy is unique in the striking sense that it is the prayer of Jesus Christ, Head of the Mystical Body. On the side of Christ, this flows from the fact that Our Lord is the only real mediator of salvation, the only Priest Who ever offered a worship worthy of God. On the side of His members, this flows from the reality of our incorporation into Christ and our participation in His Priesthood (either active or passive) achieved through the reception of indelible sacramental characters. What then can be said of a rite of Mass which, through its ecumenical orientation, implicitly denies the unique mediation of Christ? Or which obscures the essentially sacrificial aspect of that mediation?
Or which implicitly denies the hierarchy among the sacramental characters by which the members of Christ participate in and benefit from this mediation? Such a liturgy is untrue to itself. It denies its own nature and lies about its own identity. Objectively, it is an insult to the Son considered as Incarnate God.