As with any written text, some sophistication is necessary when reading the Scriptures. All or nothing approaches which hold that the Bible is to be read in an entirely literalist way, or that it is all merely symbolic, must be avoided. The more authentic question is, which texts are to be read and understood literally, and which texts employ metaphor, simile, hyperbole, or other literary techniques?
 
Thus, to cite your friend’s example, it would be strange to read Jesus literally when he says, “I am the door.” This would require us to think of Jesus as a large wooden plank, with a doorknob. It is reasonable to conclude that Jesus is speaking metaphorically when he says this, since the specific context of the saying, and the wider context of the overall Scriptures, in no way encourage us to think that Jesus spoke in a literalistic manner here.
 
When it comes to the Eucharist, however, there is a very different conclusion to be reasonably reached. When Jesus says over the bread, “this is my body,” and “this is my blood,” we are on good grounds to conclude that he is not speaking metaphorically, but literally. This is because the wider context of Scripture supplies, and insists, upon a literal interpretation.
 
In particular, Jesus insists in John 6 that the bread he gives is this true flesh for the life of the world. The Jewish people, listening to him that day, understand him to be speaking literally, and most of them scoff and murmur in protest. Though Jesus could have corrected their interpretation, and insisted he was only speaking metaphorically, he did nothing of the sort. Rather, he intensifies a literalist interpretation by insisting that they must eat his flesh, and drink his blood. Many, horrified at this, left him and would no longer walk in his company.
 
Thus, Jesus pays a rather high price, for a literal, not a metaphorical, understanding of the fact that Holy Communion is in fact a receiving of his true body and true blood.
 
St. Paul also teaches that Holy Communion is a partaking of the body and blood of Christ and goes on to insist that those who receive it unworthily, sin against the body of the Lord.
 
A final bit of contextual evidence is supplied by the fact that the early Church, as seen in the writings of the Fathers, universally understood these words in a literal way.
 
Hence we are on good ground and insisting, that the utterances of Jesus, “This is my body… This is my blood” are to be interpreted literally. This also illustrates the kind of sophistication necessary when approaching sacred Scripture.

No it is not so. Jesus actually multiplied the loaves and fishes. The “spin” given in the sermon is a rather tired and dated notion that developed in the 1970s. It has a seemingly clever insight with a moral imperative, that if we learn to share, there will always be enough.
 
But denying that a true and plainly described miracle took place is not respectful of the text. Jesus says plainly, they have no food (cf Matt 15:32). The Apostles observe the same and offer as evidence a mere five loaves and two fish. Further the texts are clear that it is from these five loaves and two fishes that Jesus feeds the multitude miraculously. The Apostles take and distribute the food from these very sources. There is no indication whatsoever that people started taking out other food that they had been hiding and learned to share.

The Catholic practice of reserving communion to fellow Catholics is fundamentally rooted in two things. First there is a norm of Scripture: A man ought to examine himself before he eats of the bread and drinks of the cup. For anyone who eats and drinks without recognizing the Body of the Lord eats and drinks judgment on himself (1 Cor 11:28-29).
 
For St. Paul, the issue is not only sin, (which might exclude some Catholics as well), but also, the need to “recognize the Body.” Yet a great majority of Protestants do not believe Holy Communion to be the Body of Christ, but only a symbol. Hence they cannot truly say the “amen” that is required to the acclamation, “The Body of Christ.” Thus, out of respect for both them and the Sacrament, we do not ask them to assent in faith to something which they regretfully do not believe.
 
A second reason for not sharing Communion is rooted in the fuller meaning of the Sacrament. In receiving Holy Communion, we do not merely speak of a personal communion of the believer with Jesus, but also of Communion with one another in the Church. But sadly, there are many things that divide Catholics and non-Catholics. In coming forward, one attests union with Jesus Christ, but also union with his Church, and all she teaches. Since this is also what Communion means, it is inappropriate for those who do not share this communion with us to come forward and signify what is not fully true, nor should we ask them to pronounce the “Amen” that affirms this community.
 
Thus, there is no rudeness intended by this practice of ours. Rather, there is a respectful, but regretful acceptance that others do not share our beliefs in certain significant matters.
 
As to dangers, note that St. Paul warns of incurring condemnation if we receive Communion either in serious sin or without discerning the Body. When we consider the meaning of our “Amen” at Communion, it is also sinful to solemnly affirm what may not in fact be believed.