I don't know what these protesters have been through in their lives, so I can't make any judgment as to whether they should be protesting, or how they choose to do it. While I personally haven't had those experiences, and choose to stand at attention with my hand over my heart, I can't say someone is wrong for doing it. If a player, or coach, or administrator, or band member, or parent wants to protest in this manner doesn't affect me. My only concern when it comes to this, honestly, is whether another official does it.
We're not there to be seen. What's the best compliment we can receive? That nobody even noticed the officials. If an official kneels, or raises his fist, or whatever, he's drawing attention to himself and (by extension) to the crew. Most likely, that attention will not be positive attention, and is going to make things tense to start the game. Things can get heated enough - we don't need to start the night with something already getting things wound up.