I will answer you. St. Pius X is teaching how we are to behave towards the Pope, and stating that if you do not treat the pope in the manner he describes it means that you are not holy.
Now, I do not believe that those who treat the Vatican II "popes" with contempt by ignoring them, exposing them for who they are, and warning Catholics to stay away from them are lacking holiness. That is how Catholics should treat heretic antipopes.
Endemic in the principle that St. Pius X alludes to in the quote is
that the pope in question is acting as a good pope should act. He
was not a purveyor of any manner of false infallibility or papolatry
(which is a word that did not even exist in his day).
It is an error
to presume that simply on the basis that
any particular pope does not ACT like a pope that he is therefore
not the pope, any more than when your father comes home drunk
he therefore ceases to be your father.
There is even Scriptural basis for this doctrine of the Church.
Respectfully resisting the false teachings of the pope is one thing
and contemptuous disrespect is quite another. But at some point,
the menace of misunderstanding creeps in, such that it behooves
a holy Catholic to say things like "the unholy Holy Father" or "John
XXIII of infelicitous memory" or "the abominable Paul VI" or "JPII
the InGrate," or "B16 the unclean." Such terms might wake up
the listener who would otherwise not be paying any attention.
The moral crimes of these men have exceeded the limits of
reasonable reservation and hope of redemption. But they are still