I often receive correspondence from folks dealing with parish politics and music, wondering if I and others can help. Of course every situation is different and navigating these areas can be extremely tricky. The question in this case involves the propers. The pastor objects to replacing hymns with propers on grounds that people won't be able to sing the propers and they will feel left out somehow. Of course the people don't deliver the homily either (at least not usually) and no one really objects to this. The fact is that there are specific roles assigned to the choir. Deny them that role and you give them no reason to exist - and this alone takes us a long away toward understanding why choirs have been so gutted from parish life today.
The pastor in this case said that that propers violate the spirit of Sing to the Lord. In fact, Sing to the Lord is in fact very strong on full propers from the Graduale as an option. See 76. It also however, quotes the Instruction Musicam Sacram (1967) on the possibility of having people sing the propers with the choir. "The assembly of the faithful should participate in singing the Proper of the Mass as much as possible, especially through simple responses and other suitable settings.”
So it is not necessarily and either/or situation. It is true the normative form reserves the Introit antiphon for the choir alone. This is a truth that should not be forgotten no matter what else happens. However, The Anglican Use Gradual, however, can be sung by everyone. The Fr. Kelly settings are easily sung by everyone too: 1st time by choir alone, the Psalm, then 2nd time with everyone. I did this just this past Sunday as the sole cantor and it worked very well. Even singing a more complex antiphon, people can join on the Gloria Patri, which I think is what Sing and MS mean by "simple responses." Again, it is not necessarily an either or situation.
All that said, there is nothing in Sing that depreciates propers relative to hymns. This is the great merit of this document, especially as compared with the previous document, Music in Catholic Worship, which has been completely displaced and left as a relic of a regrettable era in which all order and sobriety in Catholic music was abandoned.
On the other hand, every musician must think in terms of existing opportunities. It is not necessary that all hymns be immediately replaced. One can sing the communion proper and the offertory proper, and leave a hymn at the entrance and recessional, or leave hymns to follow propers. Then the entrance antiphon can be gradually introduced. Most any celebrant can appreciate the point of having people watch the procession and sing music that requires no hymnals rather than burying their heads in a missalette.