Who Decides?

It's right there in their name: Oath Keepers. They are honor-bound to defend the Constitution. This is why they keep their Freedom of Speech and Freedom of Assembly right up there with the right to bear arms. Which is why they offer anyone who joins a chance to win a gun. A really cool gun that sounds like it could be a tank. All you have to do is join up. And keep your oath.
And what oath might that be? Well, it goes a little something like: "I, [state your name], do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; and that I will obey the orders of the President of the United States and the orders of the officers appointed over me, according to regulations and the Uniform Code of Military Justice. So help me God." If it sounds familiar, that's because it's the oath that soldiers take when they join up. This is a group of Constitution Keepers. They also welcome those who did not serve in the armed forces or law enforcement, as long as these Associate Members keep their oath. The one about upholding the Constitution. 
This was the group that was scheduled to show up in front of Maxine Waters' office in Los Angeles this past week to "conduct a peaceful protest against Maxine Waters’ inflammatory incitement of harassment and intimidation." How were they going to do that? In much the same way they have done in the past, like when they showed up in Ferguson, Missouri back in 2014 to help "keep the peace" by taking up armed positions from rooftops across the city. Much to the consternation of the active law enforcement officers who had taken an oath to serve and protect the public but were having their authority tested by members and Associate Members of the Oath Keepers.
On Friday, when it became clear that Ms. Waters would not be at her office, but that many fierce and loyal supporters of hers would be there, the Oath Keepers broke their oath about protesting in front of that office. It would seem that defending the Constitution isn't something you want to do if your hands get dirty, or if someone fights back. See, these folks who showed up instead of you have their own beliefs about the United States Constitution and are protecting it the way they know how: Freedom of Assembly, Freedom of Speech, and making a noise that sounds angry. 
Because they are. What makes the Constitution work is not the defense of it, but the exercise of it. Even if that does include burning a flag. You don't have to like it, but you do have to deal with it.