Congregational singing is encouraged     

Sacred music, being a complementary part of the solemn liturgy, participates in the general scope of the liturgy, which is the glory of God and the sanctification and edification of the faithful.    - Motu Proprio,  Pope Pious X

According to Joseph Jungmann:  "music is not merely addition to and adornment of the liturgy; it is itself liturgy, an integrating element, which belongs to the complete form of the liturgy." 

In other words, you do not sing at MASS. 

You sing the MASS. 

Therefore the Eucharistic Acclamations, whether they come from Mass of Spirit and Grace, Mass of St Francis, or Belmont Mass (sung during Advent and Lent) are just one of many ways parishioners actively participate in the liturgy.  

Other ways include singing the sung responses to the celebrant's "The Lord be with you"... to which you respond..."and with your spirit"....    or singing the Psalm Responses and Gospel Acclamation. 

And of course you are free to abstain from singing if you prefer to worship silently. 

The old maxim, however, comes to mind: 

"He who sings, prays twice."  

If sung “well” (with sincerity and love), the words of a practitioner’s prayer
and the music they sing each simultaneously constitute acts of worship.

In fact, they form a gestalt expression of devotion, the whole becoming greater than the sum of its parts. This merger is so effective that the “… combination of sacred music and words, … forms a necessary or integral part of solemn liturgy.”