Public School Principal asks Police Officer not to wear his uniform when he drops off his daughter at her elementary school

How can anyone feel threatened by a police officer wearing his gun?  Do they really believe that a police officer will start attacking people?  Presumably this type of reaction is just an extremely rare event (after all there are a lot of public schools in the US), but it would be nice if the government applied zero tolerance to these events.  It seems that parents should be thankful that a police officer is taking the time to be around the school.  The only criticism that I can offer is that it would be better if the officer didn't wear his uniform but still had his gun with him.  From Fox News:

A police officer who dropped off his daughter at her Phoenix elementary school was asked by the school’s principal not to wear his uniform to the school because other parents were concerned that he was carrying a gun, MyFoxPhoenix.com reported. 

Scott Urkov is a police officer for the Coolidge Police Department. The department told him not to comment to media inquiries, but immediately after he received the no-uniform request, he posted on Facebook. 

"Nothing like your kids school calling and asking if I could not come to pick up my daughter in uniform cause parents were concerned when their kids came home telling them there was a man at school with a gun, “ he posted. “Are you freaking kidding me?" 

His daughter attends Entz Elementary School, which is in the Mesa Unified School District. . . .