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The Faith is the condition for grace; the sacraments do not sanctify in union with error.
 
The SSPX is under a practical agreement. They accept Rome’s jurisdiction. They accept Vatican II “in light of Tradition.” They declared the New Mass legitimately promulgated in 2012—and never retracted it.

That’s apostasy in practice.

> “Even if they give us everything—we refuse if they don’t convert.”
— Archbishop Lefebvre

This isn’t a question of sacraments. It’s a question of truth. You cannot drink from a poisoned well and call it grace.

I disagree that this demonstrates that one should not attend SSPX Masses. That is a gross exaggeration and distortion of the truth.
Bishop Williamson also did not adopt this extreme red light position, and I think many have fallen by the way in adopting it.
SSPX Priests are Catholic, and attending their Masses is in no way contrary to the profession of the Faith.
They do not accept Vatican II, Religious Liberty, or the New Mass: it is a very different situation from the "Indult" communities, even if the SSPX seems to be heading in that direction.
We are in a crisis. The Church even wants us to receive the sacraments from non-Catholic ministers in danger of death. Many are in danger of death if they cut themselves off from the sacraments because of this ill-conceived notion that you can't go to a Mass or receive sacraments from a priest unless he understands every aspect of the crisis as you do. It is dangerous and in my opinion not Catholic.
Of course we agree that the Resistance is right. Fortunate are those who have a Resistance priest to give them the Mass and the sacraments. But don't condemn the rest of the world to a spiritual desert.

If at this point 13 years on, you are still going to the SSPX for Mass, you really need your head checked for sanity.

Nobody who goes to the SSPX ends up staying with the resistance. They end up like frogs in boiling water, becoming liberal over time.