[GirlShortstop]

>>"As long as they accept the Pope and the authenticity of New Mass, there should not be problem."       Why should they have to accept the new mass?

For the same reason that one must accept the Most Holy Trinity.  Unity.  Catholic.  The Mystical Body of Christ can not be 'separated' into pieces as determined as 'necessary' by individuals who hold no claim to apostolic sucession.

[GirlShortstop]

The Mystical Body of Christ can not be 'separated' into pieces...

Today's reading (that I read after my post) affirms this, imo.

My beloved ones, avoid idolatry.
I am speaking as to sensible people;
judge for yourselves what I am saying.
The cup of blessing that we bless,
is it not a participation in the Blood of Christ?
The bread that we break,
is it not a participation in the Body of Christ?
Because the loaf of bread is one,
we, though many, are one Body,
for we all partake of the one loaf.

Thank you, (again!) Salvation.

[dsc]

"For the same reason that one must accept the Most Holy Trinity."

There is no equivalence between the doctrine of the Trinity and a decision by one group priests to suppress the Mass of the ages and substitute an inferior rite, born of their secular leftism.

[ultima ratio]

There is no call to be unified with novelty and error. There is one Catholic faith--and those who push for another faith are apostates, no matter how high up the ecclesiastical scale you go.

[AAABEST]

Why should they have to accept the new mass?

For the same reason that one must accept the Most Holy Trinity.

The acceptence of the rotten fruit of Vatican II is on par with adhering to the doctrine of a Triune God?

What version of the Catechism you're reading? I need to know what to stay away from.