Not at all. It would be a mortal sin for a Catholic to receive non-Catholic holy communion, just as it would be a mortal sin for a non-Catholic to partake of Holy Communion in a Catholic Church without first becoming a Catholic
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**If they did not repent in this life and make a good Confession of this sin, they would go to Hell for sure. It is a very serious matter, not to be treated lightly. **
The guidelines for receiving Communion, which are issued by the U.S. bishops and published in many missalettes, explain, "We welcome our fellow Christians to this celebration of the Eucharist as our brothers and sisters. We pray that our common baptism and the action of the Holy Spirit in this Eucharist will draw us closer to one another and begin to dispel the sad divisions which separate us. We pray that these will lessen and finally disappear, in keeping with Christ’s prayer for us ‘that they may all be one’ (John 17:21).
"Because Catholics believe that the celebration of the Eucharist is a sign of the reality of the oneness of faith, life, and worship, members of those churches with whom we are not yet fully united are ordinarily not admitted to Communion. Eucharistic sharing in exceptional circumstances by other Christians requires permission according to the directives of the diocesan bishop and the provisions of canon law. . . . "
Scripture is clear that partaking of the Eucharist is among the highest signs of Christian unity: “Because there is one bread, we who are many are one body, for we all partake of the one bread” (1 Cor. 10:17). For this reason, it is normally impossible for non-Catholic Christians to receive Holy Communion, for to do so would be to proclaim a unity to exist that, regrettably, does not.I’m sorry, but this is not what the Church teaches. There are certain conditions that can be met under which a non-Catholic can receive the Eucharist. In fact, by profession they would actually profess the very same thing that we believe and teach about it. In point of fact they would be professing Catholicism and denying their past beliefs. Furthermore. such a person would very likely be on their way into full communion with the Church.
Asserting that anyone would commit a mortal sin as you have is very much above all our pay grades.
You need to see Pope John Paul the Great’s encyclical
Ecclesia de Eucharistia and most expecially
CHAPTER FOUR THE EUCHARIST AND ECCLESIAL COMMUNION with attention to sections 43 - 46 which cover this very specifically.
I would never encourage a n-C to receive the Eucharist, nor would I, or any member of my Catholic family ever take communion in an n-C service, no matter the circumstances, if for no other reason than it would give scandalous false witness that I believe as they do and share a communion with them that I do not. There is more than enough confusion between us that we do not need to ever add more to it with something like this…and the Eucharist is far too precious.