The big problem that the RCC runs into with John 6 is that the entire chapter cannot be taken literally. It works allegorically, but not literally.
But to try to interpret a passage allegorically, then literally, then again allegorically, then literally, and so on, picking and choosing on a verse by verse basis which ones to interpret which way, is extremely poor exegesis.
Rather than using Scripture to determine doctrine, it smacks of cherry picking verses to support already predetermined doctrine.
Funny you should put it that way...
While Catholics believe the Bible is inspired by the Holy Spirit and that it is true, one cannot take individual biblical quotes or passages and say each one is literally true, Pope Benedict XVI said....In his message, the Pope said clearer explanations about the Catholic position on the divine inspiration and truth of the Bible were important because some people seem to treat the Scriptures simply as literature, while others believe that each line was dictated by the Holy Spirit and is literally true. Neither position is Catholic, the Pope said.
-- from the thread How to Read the Bible as a Catholic [How? Don't take indv. verses as "literally true", says Pope]
I 'literally' don't know why SO many folks just can't take 2 verses LITERALLY:
John 6:28-29
Then they asked him, “What must we do to do the works God requires?”
Jesus answered, “The work of God is this: to believe in the one he has sent.”