Reading the article, and some others, possibly the dad encouraged him to do the protest.
Certainly the young man and his family have every right to protest in whatever way they care to and wherever they might feel the urge. They have that right as a US citizen. The First amendment is in fact the first for a reason. I many not agree with his protest, but he does have the right to protest.
The problem is that the Cub is in fact representing not only his pack, but his Charted organization, his district, his council, and the BSA in general. If he wants to protest the pledge of allegi