We should take it easy on the rent-a-cops for now, I'm a rent-a-cop, and often times if there are instructions from higher-ups you follow them even if they are completely ridiculus. My guess is that the guards were probably instructed to ask anyone carrying signs, wearing clothes, ect. to further the peace movement to leave...even if he was just sitting there, sometimes its hard to use discretion when you're a measly security guard and could be fired if someone misinterpreted you not confronting the man to laziness or inability to follow instructions. But in this case, its gonna fall on the guards no matter what even if it isn't their faults...here's a little story unrelated, but tells the struggles of a security guard.
At my job there are certain times when guards go on "rounds" during this time the doors have to be locked at the entrance if we're not sitting there to watch it. So we lock the doors, go on our rounds like instructed too and get back to find parents waiting in the lobby to pick up their kids, they are furious that they had to wait 15 min. , so they complain to human resources, human resources yells at us. So in the future we wait and wait and wait until every parent has come to pick up their child...in the meantime we've missed the oppurtunity for an evening round, and then we get into trouble for missing a round...
Being a security guard for a large company, or a mall, is tough cause there's a lot of people to answer too, and the policies are changing all the time. Securiy guards aren't allowed to use discretion the same way law enforcement can, failure to enforce the rules will result in termination. There's no letting it slide...so in defense of the security guards, lets wait to hear the rest of the story.