Before I start please realise, my brethren, that much of what folks are seeing going on in the West is NOT AT ALL what is supposed to have happened. Behind the scenes there is a quiet war going on. The council documents were abused by progressivists. They are also being abused by hard-liners who have no love for the Church. Many of us are stuck in the middle... looking helpless.
God will fix it. He always does. Let us think of the iconoclasm that happened in the East so long ago, and yet it is a painful memory to bear. Satan seeks nothing more than rid the world of the Eucharist, by doing harm to the priesthood and the Church, and the dignity and decency of our wives and daughters, who are meant to be daily reminders of the Blessed Virgin Mother of God.
With that said... the guitar is an aberration within the confines of the Most Holy Sacrifice. That is a fact. It became at once widespread. We are blessed that it is now disappearing. These 40 years after the last council have been a severe trial for many Catholics. We now have a good and holy shepherd who is strong. It is clear, to all but the most hard-hearted, that Christ finds the traditional liturgy used in the West to be a pleasing child of His, and it is seeing quite a revival. The Son of God has many children and we thank Him for it.
Catholics are generally bothered about it as much as anybody. Many loathe it. Many seek to only chant the Psalms and Canticles, which are too often replaced by music professionals who think they know what is best.
Much of the proper chant settings are available here: http://www.renegoupil.org/
"Tra le Sollecitudini" was issued by His Holiness Saint Pius X in 1903.
He reminds us that purely vocal music is the most appropriate, but that he can't force the faithful to give up organ music. Catholics are asked to limit the use of it to support the voice if used at all.
Someone in this forum said that organ music is the tradition in the West. This is not entirely accurate. It is a custom. It has grown in the last 500 years or so due to the influence of Classicalism. I must confess that many Catholics do not like organ music, especially as it is popularly employed. The traditional music of the West is chant. Gregorian chant is not the only form. I am very edified by Roman Chant (rarely heard). The chant employed is dependent upon the rite. Domincans use Domincan chant, Mozarabics use Mozarabic chant, et cetra.
Returning to and considering my words on the guitar as an aberration. I will not damn anyone to hell for using it but certainly do not find it particularly edifying. It is tragic that the insertion of pro-fane music has made it's way into God's holy temples. Pro-fane music can be good or it can be bad. But, either way, it is pro-fane and so it's home should be kept to our everyday secular life.
One might consider a proper use of the guitar to be (for example) the many Spanish and Portuguese charrangos composed in honour of Our Blessed Mother. Such a use of the guitar is honorable and it carries devotion to His Mother beyond the temple and out into the world of those who do not know her embrace.