The Cops WERE doing there job in case you didn't notice. They warned this guy that he could possibly get hurt if he went back into that event and it was also a strong possibility that a few cops would HAVE to get hurt as well when they had to go back in and save him from the crowd.
I see this differently than you because I'm married to a cop. I'd be pretty damn upset at this guy if my husband had to go in and save him from that crowd and turn around and get hurt himself.
First of all they were only saying that so because they could think of nothing else to do to stop him. They have the duty to protect every single person there, if they cannot do their job then they need to get off the force. If the force cannot do the job they need to allow a militia to be formed that will do the job.
The real deal here is that the police probably got the word from the politicos at the top and were supposed to prevent any interference at all by anyone.
We as americans lose ground more and more in our own nation each and every day. We need to stop playing around and demand that the police enforce the law, not just the laws that are being emphasized by the politicos.