This is what sede priests would like you to believe, and some of them openly admit they have no principled reason for it. They just don't want you going to the Indult, as that is a "competition" for them. As if saving souls is primarily about competition. Anyway, your opinion can be answered in various ways, but one of the shortest and simplest is from Eucharistic Miracles. A study of Eucharistic Miracles, including those that have caused Atheist Scientists to repent and become Roman Catholics, proves that the New Rites are valid. They obtain less grace from God, but sufficient grace for the Sacrament to be valid. The infallibility of the OUM proves the same. For, if 5000+ Bishops of the Universal Church use and approve these rites, it is obvious they cannot be invalid. Anyone who says otherwise doesn't realize he has denied OUM Infallibility, which was defined at Vatican I. A study of the new rites shows that they retain the parts necessary for validity. They are valid, although it is permissible to believe the Traditional Rites are objectively superior and preferred by Heaven.
"...It is not our purpose in these pages to decide whether the new ordination rite is invalid, though, as we shall see, the argument is substantial enough that we are bound to allow for this possibility.
Furthermore, we must see the issue in the context of the total redefinition and reconstitution of the Church, such as was set in motion at the Council. In view of the fact that, since the Council, the priest's role has been in the process of being modified, as we said, to that of a Protestant presbyter,
there is every reason to deduce that the new ordination rite sabotages the Sacrament of Holy Orders according to the explicit program and purposes of those now in power.
(The reader is reminded that the very doubt which this change creates serves the malevolent purposes of the conspirators as well as does the certitude of invalidity, because from the doubt flows controversy, disagreements, factions, confusion, and disquietude among the clergy and the faithful.)By way of preface, we observe: The revisers had a reason for making changes, and particular reasons for each change they made.
They cannot argue that their new formulas are identical to the old; that would be to admit that the changes mean nothing, and that, therefore, there was no reason to make them. To admit that they made changes for no reason whatsoever would be a sign of a most irreverent capriciousness and cynicism. Besides, such an explanation could only be regarded as a concealment. The new forms (Latin and English) must be seen to say something different from the old.
Furthermore, in view of what the other changes in the liturgical rites have connoted, we are compelled to be suspicious. We should rather say, we have every reason to look for an effort at neuterizing this sacramental rite, because those in charge of the new rites have shown themselves untrustworthy, or, more accurately, determinedly subversive.
The new form could not be an improvement on the old. How can one method or set of words ordain someone better than another? The alteration of the form can only have had the intention of either negating this purpose, or, at the very least, of creating a doubt as to its efficacy. (As if it needs to be said: They could not have added something to the form by taking words away. And what could they have wanted to add to the power of Orders? Why did they touch the form at all?)..." - Father Wathen, Who Shall Ascend?