I have a friend who grew up Roman Catholic but now more often attends a Protestant church. He does attend Catholic mass moderately often. He deeply resents that he is considered ineligible for the Lord's Table there, and mostly just ignores that, just going forward and receiving when he attends. He knows that it is extremely unlikely anyone there knows his history, including the priests, so... Don't Ask, Don't Tell.
He knows that I disagree with this stance. We have discussed it a few times. But let me first try to get into his head to understand his point of view rather than condemn it out-of hand. I think I can. His picture is that God Does Something* to the elements on the altar, and the priests determine who gets it. He thinks they are unreasonably interposing their judgement, however informed it is by Catholic history, and should not be denying the sacrament to those who want it. He thinks Jesus would never do that, but would offer it freely. That part is not a guess on my part. He has said that clearly. His picture of Jesus is of one open to all, but man-made rules, via the Roman Catholic hierarchy and the rules of various Protestant churches he also doesn't agree with, block those streams of living water, and are wrong to do so. He has often mentioned going to Weston Priory, in a you-can't-get-theah-from-heah part of Vermont in the 1980s, and they distributing to all who came to worship with them on a Sunday morning without question. (They also have a labyrinth you can walk. I'm just sayin'.) He thinks that is as it should be. I don't know what the official RCC position on this is and how Weston Priory does this, but I'm betting they are pretty strict about people joining their order being sussed out pretty thoroughly as Catholic and would not be flexible on the point.
I am familiar with churches that have rules of closed communion and some of their thoughts on that, and our own denomination has the communion open to all who confess Christ and intend to serve Him. The Puritans had very closed communion, wanting to have the church visible be as close to the true church as could be managed - and they were not expansive about how many they thought were getting in. Mine is not a detailed understanding of the nuances of any.
Given that picture, my friend's views make entire sense. He would add that he has never formally disavowed the Catholic Church in any way, and that he remains a good Catholic in doctrine. I would dispute that on the basis of this issue alone, but I take his point. It is true in the main.
Yet I think there is one point that changes it all. God Does Something to the elements on the altar, but he does this only in the context of a community of believers. Consider, for example, whatever it is the Mormons or the Jehovah's Witnesses do at the Table. They have many sincere seekers and decent people wanting to receive the Lord in a proper way. But I think I cannot call that a valid sacrament, however well-intended. That community cannot reliably deliver that. (Whether God does something for individuals in a given week or season I can't say. But those communities don't get enough right. I would never partake if I happened to be visiting.) The Roman Church, many Protestant, and the Eastern Orthodox and Syriac churches do not consider the sacrament valid outside their boundaries. They would draw the circle even closer. Without getting into a discussion of where exactly that circle should be drawn, I think they are applying a standard something like mine. It is not a matter of the priest or an entire hierarchy deciding who gets the goodies for good reasons or bad, but a belief that God only acts in the context of His community, for reasons we only partly understand.
So if they say "you have to be part of this community, because it is the community that provides the context, not so much what the minister says," that's quite different. I grew up Congregationalist, BTW, a group that I now think gets it all almost entirely wrong.
I wonder just in this moment if the Catholics have created some of this problem as an unfortunate tradeoff they have to make to preserve the doctrine of Real Presence. If you grew up Catholic, you were taught that, stripped of details no kid was paying attention to, God did magic up there when the priest said and did certain things, and then that was Actual Jesus, which you got to receive. That's not quite what what you were supposed to think, and it neglected all those parts about this happening only because the priest was operating from within the structure of The Church, but even as a Protestant kid growing up in a significantly Catholic city I think that's about what my friends thought, even the smart ones.
Have fun with this. It is serious stuff, but I don't have confidence I have anything more than a better-than-average understanding of it.
*The details of that are important, but not, I don't think, for this discussion.