And rightfully so. It's against the UCMJ to protest while wearing your uniform (or in any other way trying to "represent" the military or government).
Basically, these Marines have a right to protest as Joe Smith, but NOT as Cpl Smith (or whatever), which is what they're doing.
Hopefully they're stupid enough to talk, but not stupid enough to follow through with their actions. We don't need a Marine vs Police brawl in NYC. That doesn't help anyone's cause, especially when the Marines are clearly violating military law.
If these idiots served under me, I'd do everything I could to make each one of them face a courts-martial. It isn't the job of the US military to fight police, period. Even when you convince yourself that the police are just randomly attacking innocent bystanders (which, for the record, isn't true).