He participated in himself, did he ever gripe about it thereafter? 

He was referred to as a Silent Communist.

If anything the world's reaction to VII was exuberant.

Archbishop Sheen,an Enthusiast of Vatican II

https://www.traditioninaction.org/HotTopics/f041ht_Sheen_VatII.htm

Yes, Archbishop Sheen was an ecuмenist through and through.

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He was referred to as a Silent Communist.

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Bella Dodd explained that Fulton J. Sheen is the one who convinced her of the truth of the Catholic faith, so she abandoned Communism and converted to being Catholic.
Therefore, was it Sheen's "silent communism" that gave him the ability to convert a Communist?
Is that what it takes to convert a Communist, "silent communism?"

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Bella Dodd explained that Fulton J. Sheen is the one who convinced her of the truth of the Catholic faith, so she abandoned Communism and converted to being Catholic.
Therefore, was it Sheen's "silent communism" that gave him the ability to convert a Communist?
Is that what it takes to convert a Communist, "silent communism?"

Now  this may sound strange, but a teaching sister from Holy Names University in Oakland, California told me that Sisters who live in community are espousing the highest communistic ideals and Roman Catholic spirituality together. She was a devotee of Archbishop Fulton J. Sheen and the Jesuit Father Pierre Teilhard de Chardin.

I disagreed with her and told her that St. Thomas Aquinas certainly did not espouse Communism nor Socialism. Neither did St. Paul or Christ our God. Christ told us to give all our wealth to the poor and to follow Him, not Marx.

Did Thomas Merton ever abandon his Marxist ideals when he became a Catholic priest monk?

Bella Dodd told us that ever since the 1920's, there have been communist agents within Catholicism, within the priesthood, and within the convents. These priests and sisters have done much damage, especially with their influence in academia. I remember Catholic Communist activists who attended college classes with me and who were very actively promoting communism. Their favorite colors were black; they promoted race riots and anti-government demonstrations; and they had the same agenda as does Antifa today. It's been a while, so I forgot the name of their campus club, but they were able to find a priest to serve as their chaplain.

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Yes, +Sheen was certainly a Modernist after Vatican II, but no Communist.

When he narrated that famous Tridentine Mass video, he sounded thoroughly Traditional.  He made some comments in particular about the Traditional liturgical customs to the effect that the Church retains and cherishes, but does not discard, her valuable traditions.

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The resident archivist in the Los Angeles diocese for many years has been Msgr. Francis J. Weber, who knows how to offer the TLM, and did so once a month (the first Sunday of each month) to placate Catholics with a certain attachment to antiquity. He didn't have any personal yearnings for it but treated the whole affair as if it were a museum exhibit. He wasn't about to "throw away" anything in the Latin Mass, but no one thought that he "cherished" it, either, except as a showpiece. His sermons were dry and uninspiring, any reference to the liturgy or rubrics he was using being matter-of-fact and perfunctory, like giving a tour through a graveyard. He was merely going through the motions with his monthly Indult Mass. 
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There was never any sense of community there, no opportunity to socialize, no outreach program to the poor or needy, no phone tree to pass along urgent information, just the Mass, once each month --- oh, but not always. Every so often, Roger Cardinal Mahony would come in and start his unannounced custom liturgy an hour before the monthly Indult had been scheduled for, with Mahony's invited guests filling the pews on short notice. Then as the Indult congregation began to arrive, they were informed by the attendants in the Gift Shop where they had to pass through, that the Latin Mass had been canceled that week. Many of these faithful had come from many miles away, driving for an hour or more only to arrive and find out their trip was for nothing. And since the TLM was supposed to start at noon, arrivals at 11:30 am didn't have any other TLM within range they could go to instead, so they would end up missing Mass that week. Some of them would head off for Ventura, where Fr. Schell offered a TLM at the Ted Mayer Mortuary chapel every Sunday at 1:30 pm. That was 50 miles and one hour away, for some in the wrong direction. The unavoidable message was that neither Mahony nor Weber could have cared less about the TLM or the people who came to assist at it.
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She was a devotee of Archbishop Fulton J. Sheen and the Jesuit Father Pierre Teilhard de Chardin.

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Pierre Teilhard de Chardin was denied Catholic burial. Nobody Catholic wanted the likes of him in the cemetery.