This letter shows that you have put a great deal of thought and time into this issue. However, it comes across as accusatory. You use the words "ignorance" and "intolerance", which are likely to turn the principal off to the whole idea. I'd suggest getting your Language Arts teacher to read it and offer a few pointers, or I can do it for you via PM.
I hope you get to wear your kilt to the prom, and that your date is as proud of you as you will be of yourself.