I had never even heard of The Day Of Silence, and I asked my kids if they ever did it in their schools, and they said no.

I agree with you that to allow kids to walk around with tape over their mouths and refusing to speak all day during school is stupid for any cause and it is unfair to the kids who are not participating. It holds the teacher back from teaching. Nobody can answer or ask any questions.

However, you have to pick your battles. Publishing this letter is only going to cause you trouble. I would just go privately talk to the principal and tell them how you feel about it.