This has nothing to do with who it offends or who's farts you have to smell. It's about causing controversy by showing support for hatred through clothes. The little girl wearing the USMC shirt probably didn't mean to make a big political statement or support the hatred of mexicans, but a rule was made in attempt to allow everyone to co-exist peacefully for the time being and her shirt happened to get caught in the cross fire.
This isn't the case of some cook leftist principal being unpatriotic. Its a case of a principal using the authority he has to keep a race riot from happening. It sure does suck that it has come to this, but it really is an overblown issue. Things will cool down in a month and kids will be able to wear whatever they want and hate whomever they want.