If you're getting paid minimum wage in a job you hate, would you step in to help someone? I wouldn't, because I know for a fact I'd be fired for it. It is NOT in your job description to act like security.
But on the other hand, say you did step in and got pretty busted up but helped the person anyway. You think the managers are going to really be happy with you calling in sick the next day? You'd be fired because it's your own fault.
The employees are usually told to stay out of situations like this. The only one who should have stepped in was the manager, because safety is HIS responsibility.
So the employees should not be blamed for doing nothing. Except the one who recorded it, although it depends on his intention. If it was a 'LOLZ LETS PUT IT ON YOUTUBE' then yeah, fire his ass. But if it was a 'I can't step in, but I can get vital evidence on my phone' then give the guy a pat on the back for at least doing SOMETHING.
And if anyone should have stepped in, it should have been one of the customers, since they wouldn't lose their job trying to protect someone.