If they are not required by the department then it is their choice. He has every right to sit in protest, so do they.
I don't agree with either of them particularly. I don't necessarily think he should be punished by the NFL. And I do think he is being disrespectul and a jerk with the socks and not standing for the anthem. But he has every right. They want to protest his disrespect so they do it in the best way they can.
I'm not sure it IS "the best way they can".
What does it say?
1. You need us (the police) to protect you.
2. We don't like what this one guy is saying about us, and we don't like the way he's saying it. We don't care if what he's doing is legal or constitutional. We don't even care if you agree with him or not.
3. If you all want our protection, you're going to have to get rid of that guy.
4. If you don't, no protection for you!
Threats, bullying, coercion, strong-arm tactics... whatever you want to call it, it only strengthens the argument that police themselves are a part of the overall problem. Or as Kaepernick put it: "...a country that oppresses black people and people of color," ... "There are bodies in the street and people getting paid leave and getting away with murder."
These "protests" are not comparable.
On the one side you have a man choosing to sit during the anthem and wear tasteless, obnoxious socks (which are not visible from the stands). His protest is not impacting his ability to play the game, or the ability of anyone to watch him play the game. It has no measurable impact on anyone, except in the sense that now we all know what he thinks about a current topic.
On the other side we have threats of a protest action that would potentially put people's safety at risk, people who have nothing to do with whether or not Kaeparnick sits or stands. A protest action that would involve breaking contracts. A protest action which, at the very least, causes some headache for the organizers who now have to replace them.
If they wanted to stage a
comparable protest, they'd simply do something like make a point of standing in uniform with hand over heart while the anthem plays.