"Truly, truly, I say to you, he who believes has eternal life. 48 I am the bread of life. 49 Your fathers ate the manna in the wilderness, and they died. 50 This is the bread which comes down out of heaven, so that one may eat of it and not die. 51 I am the living bread that came down out of heaven; if anyone eats of this bread, he will live forever; and the bread also which I will give for the life of the world is My flesh.”
52"Then the Jews began to argue with one another, saying, “How can this man give us His flesh to eat?” 53 So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink His blood, you have no life in yourselves. 54 He who eats My flesh and drinks My blood has eternal life, and I will raise him up on the last day. 55 For My flesh is true food, and My blood is true drink. 56 He who eats My flesh and drinks My blood abides in Me, and I in him. 57 As the living Father sent Me, and I live because of the Father, so he who eats Me, he also will live because of Me. 58 This is the bread which came down out of heaven; not as the fathers ate and died; he who eats this bread will live forever.”
"59 These things He said in the synagogue as He taught in Capernaum".
"60 Therefore many of His disciples, when they heard this said, “ This is a difficult statement; who can listen to it?” 61 But Jesus, conscious that His disciples grumbled at this, said to them, “Does this cause you to stumble? 62 What then if you see the Son of Man ascending to where He was before? 63It is the Spirit who gives life; the flesh profits nothing; the words that I have spoken to you are spirit and are life. 64 But there are some of you who do not believe.” For Jesus knew from the beginning who they were who did not believe, and who it was that would betray Him. 65 And He was saying, “For this reason I have said to you, that no one can come to Me unless it has been granted him from the Father.”
So after the Jews heard Him say that He is the "bread of life" and that anyone who "eats of this bread" will have eternal life and after He tells them that "He who eats My flesh and drinks My blood has eternal life, and I will raise him up on the last day. 55 For My flesh is true food, and My blood is true drink. 56 He who eats My flesh and drinks My blood abides in Me, and I in him.", and after they became angry, we see in verse 63 that He tells them that the words He had just spoken to them were spiritual.
So, like I said, Scripture, inspired by the Holy Spirit, interprets itself. We know that the communion is not the literal flesh and blood of Jesus because He tells us Himself that those words are "spiritual".
That isn't "rejecting" His words, it is putting them in the context that He told us to put them in.
The fact that we disagree and that there are over 30,000 denominations in Christendom, differentiated by one degree or another, on the interpretation of Scripture is all the evidence one needs to reject that hypothesis.
If you go to that very revelation in John 6 you referenced Jesus had an opportunity to say that He was speaking figuratively or symbolically, like He did when He explained being Born again from above to Nicodemus, but He didn't. He reiterated the Real Presence on many occasions, most notably when He taught us how to pray. He called the "daily bread" Epiousios, a word found nowhere else in Greek literature, which is translated as supersubstantial bread and which the Early Church Fathers unanimously referred to the Eucharist. Jesus used a very emphatic means to reveal this to us. He told us what He was going to tell us. He then told us. He then told us again, and again, and again. It is only when you artificially construct the context to presume that the Eucharist cannot be the Real Presence or that Jesus' words cannot be transformative that your position appears sound.
So I will repeat my question in slightly different words, how can you on your own authority accept or reject the Real Presence?