"Mouthing the words," I suppose, if one can not read to himself without his lips moving, is OK. It indicates one is paying attention, at least.
But encouraging the entire congregation to join in with the priest in saying aloud parts of the Mass specifically proper to the priest is a different animal altogether. If we're all saying the words, why do we need a priest? If there is no difference between me saying something and a priest saying it, who needs a priest?
That is the faux "egalitarian" line of thinking behind such "innovations." It is set on destroying the distinction between priest and layman.
But you bring me to something that is fast becoming a pet peeve of mine. The crossing of the forehead, lips, and heart before the Priest or Deacon reads the Gospel. I used to think it was a fine thing to do, but I read a thread a while back that said it was nothing but aping the reader like a monkey. That made sense to me because why would I cross MY lips when somebody else is about to read. So, I cross myself while everybody else does the whole pantomime. I just wonder if it is required to do that.
This may indeed be a case where "aping" happened, but I see nothing wrong with asking for Christ to be "on your lips" even if you are not presently speaking. It is one thing for a spontaneous act of pious imitation to become part of the liturgy through years of practice.
This is why liturgy is so important. You have to nip abberent practices in the bud, or they will grow to become a norm.
I sang at the funeral of a Priest one time. It was a great experience. Archbishop DiNardo was there and I got to meet him. But the thing I wanted to mention was that all of the brothers from the guys order that could make it were there... maybe 50-75 priests, and they all came up into the Sanctuary during the Eucharist. They all said all the words of the mass so all you could hear was all of these voices doubling and overdoubling. It was a bit eerie and arcane, but I really enjoyed it.
Then they all sang Salve Regina together. It was touching. Funny, but I've been to more funerals since I've been Catholic than I've been to in my life.