The mistake you are making is that people were 'allowed.' No cops said hey parents come on down here and hang out. No one was allowed, but rather they were just there. Most of those people were there in the first few minutes and stayed until they were made to leave. In other words, in a perfect world the bystanders would have been removed immediately but oh shit lets have a conniption fit because they werent. The cops did get bystanders out of the parking lot fairly soon which is apparent from overhead shots from the helicopter with no bystanders other than first responders and offcials. It wasnt active shooter at this point or the kids wouldnt have been coming out of classrooms either. As far as EMS not being there, there was a staging area for them to be at and thats where they have to be until called for. Those bystanders dont have a staging area that they are held accountable to. EMS could have walked down there where the people were if they wanted, but they also would have possibly got written up, fired, lost license, etc for it. Ordinary bystanders dont have any worry over matters like that.