Tom, if you're like my brother-in-law or my son-in-law, you're still a marine, just an inactive one.  A short kneel and then standing would say "America has a bad problem, but I still love and respect it.". That would be acceptable and not offensive. Fist raising? Simply a show of defiance and totally okay. Arm locking? I'm all for it and it ain't in the least offensive. 

The thing is, the instigators and leaders of this very much WANT TO BE OFFENSIVE.  Their attitudes are arrogant and in-your-face, and intended to cause a huge uproar. Most of the teammates joining them are doing so because they are AFRAID to be politically incorrect by refusing to do so. It takes courage and integrity to go against the crowd when the crowd is wrong, and they simply don't have the courage and integrity to do it.