Edmundus has this discussion well in hand, and in the past I have vigorously argued the same point of view, but I will put in my two cents for now.
It is not participation if you remain silent when the assembly is expected to be making a response or singing a hymn. The silence of participation refers to the times when we should be listening and reflecting on the parts said by others in the liturgy. For example, the readings. We should not be reciting the Scriptural readings along with the lector and the deacon, we should be respectfully silent as we absorb the meaning and symbolism of the readings. We should also be actively silent during the homily, unless of course the priest demands some interaction from us: he could ask a question or for a show of hands. Otherwise we are required to cede the floor to him as he teaches us the Word. Likewise, the presidential prayers such as the Eucharistic Prayer. No lay person should be “participating” by reciting the words proper to the priest. It is his sacrifice and his prayer and we are actively participating by joining our hearts and minds to his prayer in silence.
In contrast, we must, as Edmundus points out, be of one heart and mind when verbal participation is called for. What would the Mass be if the people conspired to remain silent during the Creed? Or the Kyrie Eleison? Would an observer not see that we are being disrespectful to the presider and to God, and perhaps not so faithful as we claim if we cannot be bothered to recite the words proper to our liturgical role? What kind of Mass would we have if the priest refused to recite the Eucharistic Prayer? It is not optional to say the responses and it is not optional to sing when words and/or music have been provided to us and the cantor or choir is striving to lead us in prayerful song.
It is disrespectful and uncharitable to God for us to refuse to join others in song. It is also disrespectful to the priest and to the musicians who work hard and put our blood, sweat and tears into the ministry of the Word to ensure that God is glorified when the people sing together. The function of music in the liturgy is not mere entertainment or profane enjoyment subject to our tastes and whims. Music serves a threefold purpose: it is pastoral, liturgical, and evangelical. By singing hymns we not only glorify God but we teach each other in catechesis when hymns are rooted in Scripture and doctrine. We also spread the Gospel by repetition of phrases that tell of God and His good works. Why any good Catholic would refuse to glorify God or refuse to spread His Gospel message is truly beyond me. It does not make sense that anyone should suggest that an integral part of the liturgy should be ripped apart and made optional so that anyone who got up on the wrong side of the bed can freely refuse to take part without any repercussions.
Scripture and Tradition and the binding liturgical documents are all very clear that singing is an integral part of the liturgy that has true benefits for the faithful and must be encouraged and fostered in all the people of God. Those who say that silence is acceptable are cherry-picking and prooftexting to twist the mind of the Church into something that she does not intend. Those of you who claim to sing badly should put some effort into learning. Singing well has little to do with talent and is all about applying yourself to the technical details. It can easily be taught and learned by almost anyone without a disability. Don’t sell yourself short, and don’t disappoint God, who has commanded us to make a joyful noise.
