I understand the argument offered for metaphor. The reason shrugging it off as metaphor doesn't work for Catholics is because Jesus said something very hard to accept--so hard that many left him. To them, it was no metaphor--and it wasn't to Peter, either. He, however, maintained his trust in Jesus and in the hard truths that he taught.
Those that left left because they couldn't stomach what seemed like the crazy talk of a madman. Peter remained because he and the others who remained were given a rational explanation, flesh was a metaphor for teaching, nothing too hard nor too difficult to swallow about that..
Furthermore, If Christ's words are eternal life, then when Jesus broke the bread and said, "Take and eat--this is my body," do you believe that metaphorically Jesus was saying the bread was a substitute for his actual words (since you believe that is the reasonable explanation that can be deduced from John 6:68)? Why would Jesus pile on awkward metaphor upon difficult to understand metaphor? Why not say, "By hearing and acting upon upon my words you are consuming me, and you will have eternal life?"
You have failed to include in your speculations that Jesus was on a mission from God who told him what to say and how to say it. Why did he speak in parables and metaphors? To teach people how to understand the language of the prophets who spoke for God so they could access a treasure of incalculable value that was buried and hidden for thousands of years in the fantastical stories and figurative language used in the OT.
Jesus said that unless you eat his flesh and drink his blood you can have no life in you. His flesh, teaching, is about how to correctly understand the figurative language used in the law that reveals hidden subjects. The promise for compliance with the law is eternal life. Because Jesus taught the only right way to understand and comply with the laws demands that results in the promise of eternal life fulfilled his words are words of eternal life.
Why offer bread saying, "This is my body" and wine saying, "This is my blood"? .
Why? Excellent question.
Jesus repeatedly warned his disciples about a test according to scripture. He told them to be careful how they listen (Luke 8:18). He berated them saying, "How can you fail to see that I was not speaking about bread? (Mat 16:11). He compared himself to the serpent that Moses lifted up during the time of testing in the wilderness. He admonished his disciples to
stay awake and pray to be spared the test in Gethsemane where Jesus prayed to God for him to change his mind about some unspecified cup.
The warnings are actually intended for the reader.
Take from my hand this cup of fiery wine and make all the nations to whom I send you drink it. When they have drunk it they will vomit and go mad; such is the sword that I am sending among them. Jeremiah 25:15
I will force your oppressors to eat their own flesh and make them drunk on their own blood as if with new wine. Isaiah 49:26
From his mouth there went a sharp sword
with which to smite the nations. Rev 19:15
I understand why you hold the variant belief. That belief just doesn't work for many of us. It tries to scoot around scripture,
No, you do not understand. You cannot understand. You worship the lifeless work of human hands and then eat it for spiritual life.
If scripture is true, you died a very, very, long time ago. Your putrefied flesh is vile and contaminating. Can't you smell that smell?
Do yourself a favor and go back to the drawing board.
Humble yourself and re-read everything in scripture as if you were a little child about to read a fairy tale for the very first time knowing that it has a hidden teaching and then look and look and keep on looking for that teaching until you find it as if your life depended on it. It does.
Maybe then you will notice that only in the gospel of John any talk about eating flesh and drinking blood happened before the last supper and during the last supper the only one given bread, dipped in wine, was Judas as the way that Jesus identified his betrayer to everyone else..This is no accidental discrepancy.
Remember? As soon as Judas received the bread, Satan entered him. (John 13:27)