"What is it about this paragraph that should give concern to the faithful Catholic?"
The first offending phrase is:
"Since the Church is in Christ like a sacrament or as a sign and instrument both of a very closely knit union with God and of the unity of the whole human race..."
Firstly we have the novel idea of the Church being referred to as being "like a sacrament". This is not necessarily problematic in itself, but it is a novel use of the word "sacrament" in Catholic theology - it is introduced without any citation or source from Scripture or Tradition to support it. The translation here is much toned down from Flannery's edition which states "the Church, in Christ, IS IN THE NATURE OF SACRAMENT.."
The expression introduces a new meaning for the word "sacrament" without any justification or explanation. It is ripe for future corruption, distortion and misinterpretatrion.
Also you have this ambiguous expression "is IN CHRIST like a sacrament" - can the Church not be in Christ? Does the Church extend its borders outside of Christ? Does she have an existence apart from Him?
But the novel use of the term "sacrament" serves to hide and distract one's attention from the most dangerous part of this sentence. This is where we see the theology of Karl Rahner infiltrating the document right at the outset and providing a "time-bomb" which the modernists will return to later. It is the clause:
"a sign and instrument.(..).of the unity of the whole human race".
Here we have both a novel and erroneous idea of the purpose of the Church. It is quite nonsense to claim that the Church is an instrument of the "unity of the whole human race". Implicitly it introduces the heresy of universalism into the document, and it also implicitly denies the following Catholic doctrines:
a) Predestination - the Church is only an instrument of unity of the elect, not the whole human race. She is actually a sign and instrument of division between the elect and the reprobate.
b) The existence of hell and damnation - we know from Scripture that hell is already populated and that many more, maybe most, will go there. If the Church is an instrument of unity of the WHOLE human race, then we would have to deny that anyone is in hell.
c) The City of God and the city of satan - the opposition of the Church and "the world" are implicitly denied. Thus the ground is laid for the opening up of the Church to infiltration by the world and its prince. It flies in the face of the admonitions of Scripture and the attitude pervades most of the council's documents.
d) Extra Ecclesiam nulla salus.
It thus sets the scene for the whole subsequent syncretistic, "one world religion" theology of the modernists that has poured into the Church in the wake of the council.
The second offending phrase is:
"The present- day conditions of the world add greater urgency to this work of the Church so that all men, joined more closely today by various social, technical and cultural ties, might also attain fuller unity in Christ."
Here we see "unity in Christ" being treated as some kind of extension of a "unity" that results from "social, technical and cultural ties" - a naturalistic conception of unity which is primarily anthropocentric rather than theocentric. It is some kind of unity which man is building by his own power rather than a unity which comes as a result of communion with God. Unity in Christ is thus just an extension of this "natural unity".
Again, the groundwork is being laid for the naturalistic one-world-religionists. Quite apart from which, the analysis that "all men" are being "joined more closely today" is surely suspect when, in fact, social and cultural disintegration were/are the order of the day rather than social and cultural cohesion.
Taking the last part of your essay first, you're misreading the sentence on unity. You've given it a meaning that isn't there.
"The present- day conditions of the world add greater urgency to this work of the Church so that all men, joined more closely today by various social, technical and cultural ties, might also attain fuller unity in Christ."
In no way can this sentence be interpreted as meaning that unity in Christ is simply a result of, or an extension of unity resulting from technical or cultural ties. On the contrary. It means the opposite. The sentence states clearly that these pre-existing cultural and technological ties make the work of the Church- what?? Yes, that's right-more urgent.
Surely urgency would be less of a necessity for the Church if that technological and cultural unity already existing naturally gave rise to unity in Christ? The writer is saying "no". The work of the Church is now more urgent than ever.
I see no indication whatsoever that there is a sequential connection between the two things in terms of one leading naturally to the other. Rather, I see the writer saying that the social human unity places even more demands on the Church and its spreading of its message.
As for the word "sacrament", the strict definition is "an outward sign of inner grace." However, my Catholic Encyclopedia also tells me:
Taking the word "sacrament" in its broadest sense, as the sign of something sacred and hidden (the Greek word is "mystery"), we can say that the whole world is a vast sacramental system, in that material things are unto men the signs of things spiritual and sacred, even of the Divinity. "The heavens show forth the glory of God, and the firmament declareth the work of his hands" (Ps. xviii, 2). The invisible things of him [i.e. God], from the creation of the world, are clearly seen, being understood by the things that are made; his eternal power also, and divinity" (Rom., i, 20).
One who defines "sacrament" only in its narrowest sense, will naturally take issue with the use of it in its broadest sense, which is what the Vatican document does-and let it be said rightly so. It is the preamble to a long document- preambles are when subject matter is introduced and terms and subject matter are generally defined in their broadest sense.
Finally, to claim that the Church is "a sign and instrument" of the "unity of the whole human race" does not deny Church teaching on any of the issues you list.
The unity spoken of in the passage is not a unity which results from all accepting Christ and obtaining salvation and none being damned. Rather it is a unity which results from the fact that:
Man is a creature of God in a created universe. All things that are, except Himself, exist in virtue of a unique creative act. Catholic Encyclpedia
The Church, being commissioned by Christ, to "make disciples of all nations", is indeed that sign and instrument.