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Vatican II is not infallible, there is nothing de fide defined in it. But yes, Vatican II can contain no heresy, otherwise the Church defected in 1965. Those who say otherwise are mistaken. Pope Pius IX said clearly in Etsi Multa that to say a Council fell into heresy denies Church indefectibility. But there are lot of grades of theological certitude between "de fide" and "heresy". Two main things in Vatican II are "ecuмenism" and "interfaith dialogue", these are not defined in strict terms at all. They are merely pastoral proposals. If anything is de fide with respect to them, it is de fide that we can and should work for the conversion of the separated to the Catholic Church.
His Excellency Bishop Fellay docuмents that many Bishops consider many points of Vatican II to be "open questions": ""And then, from time to time, I receive letters. Like this one: I will read it to you in English because it is an image:

“Stick to your guns. Always stick to your guns.” This means: Keep your hands on your revolvers. Hold them firmly. In other words: “Defend yourselves. Always. And refuse to compromise in these matters that do not really pertain to the substance of the faith: religious liberty, ecuмenism, dialogue with non-Christian religions. There are many of us in the hierarchy who think and believe in what you are doing about these questions.” It is a bishop who wrote that to me. He does not write “I”, he writes that there are many of “us”. He wrote other things too that I dare not read to you, they are so laudatory ... “Come to our aid.” And also: “Do not let go of anything, continue like this, we need it!” This is new! There was nothing like this before! The bishops used to tell us: obviously there are problems, but at the end of the day.... And here they are telling us: “Resist, we need it!” Actually they do not speak too loud because they know very well that if they do, they will be cutting off their own heads ... I am not telling you their names because we do not want to burn out these prelates, but there are several of them.

I discover some, just like that, by surprise, and there are a certain number of them! And these are young bishops! And some of them were appointed by Pope Francis! He is not just appointing bad ones! He is all mixed up, like his whole attitude, which has also increased the general confusion. But it is extremely interesting to see that there is this movement, and I am certain that it will no longer stop. Why? Because these bishops see where the truth is, and they will not give in. They are annoyed, they are cornered, because they are in the system, but they will no longer give in. Just like these priests who have discovered the old Mass, they will do all that they can, they are annoyed, cornered, but they will keep it. These are skirmishes that have been won." http://fsspx.asia/en/content/23944

And as mentioned here, http://catholicismhastheanswer.com/vatican-ii-must-be-clarified/ Vatican II is non-infallible, so lesser error than strict heresy is possible in theory. "Moreover, let us not forget that the canons of the Council of Trent and of Vatican I are de fide, whereas none of the decrees of Vatican II are de fide;The Second Vatican Council was pastoral in nature."- Dietrich Von Hildebrand. "The Second Vatican Council has not been treated as a part of the entire living Tradition of the Church, but as an end of Tradition, a new start from zero. The truth is that this particular Council defined no dogma at all, and deliberately chose to remain on a modest level, as a merely pastoral council; and yet many treat it as though it had made itself into a sort of superdogma which takes away the importance of all the rest."  -Cardinal Ratzinger (Now Pope Benedict XVI), address to the Chilean Bishops, 13 July 1988, Santiago Chile

Also, Bishop Fellay said the Society Bishops, from the Holy Year forward, now have Ordinary Jurisdiction themselves: "As a result of the Pope’s act, during the Holy Year, we will have ordinary jurisdiction. In the image I mentioned, this has the effect of giving us the official insignia of firefighters, whereas such a status was denied us for decades. In itself, it adds nothing new for the Society, its members, or its faithful. Yet this ordinary jurisdiction will perhaps reassure people who are uneasy or others who until now did not dare to approach us."  From: https://damselofthefaith.wordpress.com/2015/12/01/ordinary-jurisdiction-for-the-year-of-mercy-bishop-fellay-says/

So it's not true that every Bishop with Ordinary Jurisdiction in the Latin Church offers the New Mass today. The New Mass is a vastly inferior form of the Mass; it is truncated, partial and extrinsically deficient in comparison to the Traditional Mass, the True Mass of the Roman Rite. A new Mass would have at most like 1/100th of the Graces of the True Mass. Every well-informed Priest and Bishop should therefore make the decision to offer the TLM instead. After Summorum Pontificuм in 2007 and Universae Ecclesiae in 2011, it is quite possible for every Bishop to do this.  But it is neither invalid nor a Black Mass nor heretical, as +ABL also said in the 1980 letter to the Holy See cited earlier.

Bp. Huonder is also another diocesan Bishop or Ordinary who is now, by the Grace of God, going to be offering the TLM exclusively.

Vatican II is not infallible, there is nothing de fide defined in it. But yes, Vatican II can contain no heresy, otherwise the Church defected in 1965. Those who say otherwise are mistaken. Pope Pius IX said clearly in Etsi Multa that to say a Council fell into heresy denies Church indefectibility.