why I'm against banning cell phones at school

Because of times like this:

Police say they have arrested 16-year-old student at Todd Beamer High School and found three loaded guns plus extra ammunition Thursday.

The emergency prompted a lockdown of the school during afternoon classes....

Diane Turner of the Federal Way School District says a student text messaged their parent that another student had brought a weapon to school.

The parent contacted the school. A resource officer pulled the boy out of class.

Stacy Flores of Federal Way Police [says] the guns were stolen this morning in a burglary in Pierce County. She says the student was planning to sell the guns, not to use them.