Because it wont only be the person close enough to identify the aggressor that will be shooting. It is the jackass in the back row that will also get into the fray.
For the record, I saw batman last night at Mall of GA and I was carrying my LCP.
The sad fact that none of the politicos will acknowledge is that crimes like this are just about unpreventable. From the sounds of it, this was a well planned attack in which he expected to die in. If there was security that prevented him from getting into the theater, he could have just as easily hit them on the way out.