it's really hard to justify the inappropriateness of a piece based on the music alone,

Almost every Catholic spiritual master has warned about not relying on pleasant emotions as a mark of or guide to spiritual experience or progress.

One of the unique virtues of chant is that it is not emotionally manipulative music. Chant allows the text, the Word of God, to speak to the soul in a profound way, a serene way, by elevating the Word above mere recitation, using music as the means to invite and promote reflection on the text intellectually instead of responding emotionally to the music's rhythm and mood.

Can you spell out why "Go Make a Difference" has no place in Mass?

It's probably a mere matter of taste.

starting with things I learned to love in libraries (Robert Burns poetry and settings of his texts), classes (Berg's Wozzeck), non-Catholic churches (Hillsong), concert going (Miley Cyrus' Party in the USA), and early music festivals (chanson de geste), and then searching out loopholes as needed.

Focusing merely on ancient chant and pipe organ are dead ends.

In other words, many church musicians lack imagination cum talent.
That makes them angry, boring, and (hopefully) replaceable.

God doesn't care about the genre, the timbre, the medium.
The Church doesn't, either.

Papal Letter to the Cardinal Vicar of Rome – December 8, 1903

Among the cares of the pastoral office, not only of this Supreme Chair, which We, though unworthy, occupy through the inscrutable dispositions of Providence, but of every local church, a leading one is without question that of maintaining and promoting the decorum of the House of God in which the august mysteries of religion are celebrated, and where the Christian people assemble to receive the grace of the Sacraments, to assist at the Holy Sacrifice of the Altar, to adore the most august Sacrament of the Lord’s Body and to unite in the common prayer of the Church in the public and solemn liturgical offices. Nothing should have place, therefore, in the temple calculated to disturb or even merely to diminish the piety and devotion of the faithful, nothing that may give reasonable cause for disgust or scandal, nothing, above all, which directly offends the decorum and sanctity of the sacred functions and is thus unworthy of the House of Prayer and of the Majesty of God. We do not touch separately on the abuses in this matter which may arise. Today Our attention is directed to one of the most common of them, one of the most difficult to eradicate, and the existence of which is sometimes to be deplored in places where everything else is deserving of the highest praise — the beauty and sumptuousness of the temple, the splendor and the accurate performance of the ceremonies, the attendance of the clergy, the gravity and piety of the officiating ministers. Such is the abuse affecting sacred chant and music. And indeed, whether it is owing to the very nature of this art, fluctuating and variable as it is in itself, or to the succeeding changes in tastes and habits with the course of time, or to the fatal influence exercised on sacred art by profane and theatrical art, or to the pleasure that music directly produces, and that is not always easily contained within the right limits, or finally to the many prejudices on the matter, so lightly introduced and so tenaciously maintained even among responsible and pious persons, the fact remains that there is a general tendency to deviate from the right rule, prescribed by the end for which art is admitted to the service of public worship and which is set forth very clearly in the ecclesiastical Canons, in the Ordinances of the General and Provincial Councils, in the prescriptions which have at various times emanated from the Sacred Roman Congregations, and from Our Predecessors the Sovereign Pontiffs.

It is with real satisfaction that We acknowledge the large amount of good that has been effected in this respect during the last decade in this Our fostering city of Rome, and in many churches in Our country, but in a more especial way among some nations in which illustrious men, full of zeal for the worship of God, have, with the approval of the Holy See and under the direction of the Bishops, united in flourishing Societies and restored sacred music to the fullest honor in all their churches and chapels. Still the good work that has been done is very far indeed from being common to all, and when We consult Our own personal experience and take into account the great number of complaints that have reached Us during the short time that has elapsed since it pleased the Lord to elevate Our humility to the supreme summit of the Roman Pontificate, We consider it Our first duty, without further delay, to raise Our voice at once in reproof and condemnation of all that is seen to be out of harmony with the right rule above indicated, in the functions of public worship and in the performance of the ecclesiastical offices. Filled as We are with a most ardent desire to see the true Christian spirit flourish in every respect and be preserved by all the faithful, We deem it necessary to provide before anything else for the sanctity and dignity of the temple, in which the faithful assemble for no other object than that of acquiring this spirit from its foremost and indispensable font, which is the active participation in the most holy mysteries and in the public and solemn prayer of the Church. And it is vain to hope that the blessing of heaven will descend abundantly upon us, when our homage to the Most High, instead of ascending in the odor of sweetness, puts into the hand of the Lord the scourges wherewith of old the Divine Redeemer drove the unworthy profaners from the Temple.

Hence, in order that no one for the future may be able to plead in excuse that he did not clearly understand his duty and that all vagueness may be eliminated from the interpretation of matters which have already been commanded, We have deemed it expedient to point out briefly the principles regulating sacred music in the functions of public worship, and to gather together in a general survey the principal prescriptions of the Church against the more common abuses in this subject. We do therefore publish, motu proprio and with certain knowledge, Our present Instruction to which, as to a juridical code of sacred music (quasi a codice giuridice della musica sacra), We will with the fullness of Our Apostolic Authority that the force of law be given, and We do by Our present handwriting impose its scrupulous observance on all.