Yes, communion is based on Eucharist!
Now, let’s turn it around a little.
This seems to be a particular skill of yours.
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If someone comes to you and says, "no, communion is not based on Eucharist, it is based on people completely in agreement with all the teachings of the Church", would you think of the person having some kind of negative "heterodoxy". How would you feel about his unsupported approach? Would you shake his hand as a fellow Catholic? You would, right?
We have a different understanding of the nature of Eucharist.
For Catholics, participation in Eucharist is an affirmation that we receive and assent to all that Jesus did and taught. This is what it means to be “in Christ”. There is no separation between being in unity with the person of Christ, and following His commandments. He taught that, if we love Him, we will keep his commandments.
Shaking hands with other persons who claim they are Catholic does not create communion either.
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Fr. Anthony de Mello said, "God loves you at least as much as the person who loves you most."
Jesus said: Matthew 25:40New International Version (NIV)
40 “The King will reply, ‘Truly I tell you, whatever you did for one of the least of these brothers and sisters of mine, you did for me.’
This passage is addressed to believers, not unbelievers. Jesus also said that humans, being evil, could still give good gifts to their children (and do good works in the world).
Doing good works does not earn one a place in heaven.
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So, lets say a person poor, imprisoned, sick, or hungry is a "lukewarm Catholic". Now, are we called to "spit out" this person, or are we to serve him, to care for him? Do you see that such literal interpretations that may appear contradictory to unconditional love must be examined carefully? Does such "spitting out" reflect God's understanding, forgiveness, and mercy?
It is quite possible to love and serve those who are unbelievers or who have lost their Catholicity. It does not mean we are in communion with one another. Communion is not based on warm fuzzies, but in our relationship with Christ. The Holy Spirit creates communion between us as we are in right relationship with Him.
Are you frustrated, disappointed, with “lukewarm Catholics”, guanophore? It’s okay to be frustrated. All of us have had times of such “lukewarmness”, have we not, where we fall short of having great zeal for Christ and His message?
I don’t really spend much mental/emotional energy on the attitudes in the hearts of others. My responsibility is to keep myself from being lukewarm. Lukewarmness is much more broad and severe than “falling short” once in a while. It is a lifestyle that does not have a great deal of zeal for Christ and His message.
Here is a suggestion:… He wants us to focus the attention of our conscience onto our worldly comfort. You can catalog that under “OneSheep’s commentary on Revelations 3:15-17”

I know, you would not be first in line to buy the commentary.
I will catalog your belief that God wnts us to focus our conscience on our worldly comfort.
You are right, I will not be looking to buy your commentary.
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So, are you saying that people who do not agree with all the Church's teachings, even though they receive Eucharist and are inclined toward the Church are excommunicating themselves?
Eucharist is not for those who are “inclined toward the Church”, but for those who have already embraced her. Persons who are in open dissention against the teachings of the church commit sacrelege by attempting to participate in Eucharist.
Some Catholics have already excommuniated them selves under latae sententiae. Certain actions contain excommunication, so a person excommunicates themselves when they engage in the act. The Code of Canon Law, which binds Catholics of the Latin Church, inflicts latae sententiae censures for certain actions, so it would depend upon the type of dissention and the manner in which it occurred.
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Communion as upheld by individual Catholics, a real experienced community, is a phenomenon that is unquestionably influenced by our feelings toward one another.
“Communion as upheld by individual Catholics”??!!!
It sounds like a little gathering you have in your front room?
Undoubtedly most human activiies that occur in groups will be influenced by our feelings for one another. So, are you saying that you share a “communion” with other individual Catholics that all get together and experience warm fuzzy feelings with one another?