I think there are two issues that need to be addressed here with you.
First, That Paul puts no stock in the 'real presence' for one does not preclude his belief in same fore the other. Indeed, I find it strange you seem to look past Paul's comment about participating in the body and blood without any recognition those words have meaning.
Next, many non-Catholics don't seem to be able to break out (in the intellectual sense) of the fact Catholics do not accept the scriptures as the sole source of special revelation.
The doctrine of the Real Presence, like the doctrine of the Trinity, does not rest on scripture, but on Sacred Tradition, and is equally inscrutable. So while no one is denying our Lord's use of metaphors, one of the tasks of the Church is to identify and clarify those things in scripture which can be twisted to destruction.
“First, That Paul puts no stock in the ‘real presence’ for one does not preclude his belief in same fore the other.”
It does not preclude, but in the absence of other information, it is an indicator. He uses the same sort of language for sacrifices to idols as he does to the Eucharist:
“The cup of blessing that we bless, is it not a participation in the blood of Christ? The bread that we break, is it not a participation in the body of Christ? 17Because there is one bread, we who are many are one body, for we all partake of the one bread. 18Consider the people of Israel: are not those who eat the sacrifices participants in the altar? 19What do I imply then? That food offered to idols is anything, or that an idol is anything? 20No, I imply that what pagans sacrifice they offer to demons and not to God. I do not want you to be participants with demons. 21 You cannot drink the cup of the Lord and the cup of demons. You cannot partake of the table of the Lord and the table of demons.”
“I find it strange you seem to look past Paul’s comment about participating in the body and blood without any recognition those words have meaning.”
And what does it mean to eat without discerning the body? Just before that verse, we find:
“For, in the first place, when you come together as a church, I hear that there are divisions among you. And I believe it in part, 19for there must be factions among you in order that those who are genuine among you may be recognized. 20When you come together, it is not the Lord’s supper that you eat. 21For in eating, each one goes ahead with his own meal. One goes hungry, another gets drunk. 22What! Do you not have houses to eat and drink in? Or do you despise the church of God and humiliate those who have nothing? What shall I say to you? Shall I commend you in this? No, I will not.”
The congregation is the body of Christ. Yet the Corinthians are split by factions, as though the body of Christ can be split! When they meet, they acts as individuals instead of one body. Each eats when and what he wants, and the rich humiliate the poor.
In the next chapter, Paul continues to talk about the congregation as the body of Christ, with the Spirit giving gifts as He desires, but all needing each other together.
Paul isn’t talking about the physical body of Christ, but the Church - the Body of Christ - and unity, and love, and caring for one another, and using gifts to build up the body, not the individual. When they have factions in the congregation, and treat each other shabbily, partake of the Eucharist like every man for himself and aspire to gifts that build up the individual but not the whole, they fail to discern the body of Christ - the Church.
It isn’t that they fail to discern the physical body of Jesus hiding in the accident of bread, but that they fail to discern that they are one body, the body of Christ. It is the reality of the Church that they are missing, not transubstantiation.
“Catholics do not accept the scriptures as the sole source of special revelation.”
Understood. Yet Paul said he had taught the “full counsel of God”, and John wrote that “Everyone who goes on ahead and does not abide in the teaching of Christ, does not have God. Whoever abides in the teaching has both the Father and the Son.”
So how have you developed doctrine from sacred tradition hundreds or a thousand years after the Apostles? John said to ABIDE, and not to GO ON AHEAD.
Yet the Catholic Church has gone ahead and developed what the Apostles did not know. And John goes on to write, “If anyone comes to you and does not bring this teaching, do not receive him into your house or give him any greeting, 11for whoever greets him takes part in his wicked works.”