You have to understand what they see as a threat to them. First of all you are 'breaking a rule' one of their rules for that matter. I'm sure the rule was made by a school district's network administrator or someone a bit lower then that. The teachers / principal just have to follow the disciplinary route because they don't understand what you are doing. When someone doesn't know what you are doing, they start getting uneasy with you. Even though you view yourself as a responsible computer kid thats definately not what most adults will view you as when you are doing something they do not recognize on a computer. I recognize the condescending feel that adults give you especially when they don't know what you do about computers.

I personally have encountered this, but I had connections with certain people in the [schools] administration that knew how positive my actions were. You may not have that luxury, and can get nailed if you don't. Luckily you got off with supervised use, I know a handful of people who thought they were hot shit always talking me down because of this or that. I chuckled while I sat back and they got busted.

being in a network administration class doesn't mean you can compromise the school districts "Internet code of conduct" though. Not in the eyes of the ones who discipline you [ teachers and or principal, etc. ].

I have a question though: who were those emails to? the company that owns the filtering software? or the school districts admin?