Good points. Thank you for speaking up.
I would slightly differ with you in that it should be voluntary for teachers to carry a firearm. As others have stated, only those who voluntarily take on the responsibility can be expected to use a firearm. By making it clear that teacher carry is voluntary we also do away with the crazy image of a gun-hating teacher having a firearm thrust upon them. Allowing teachers to carry is still going to sound crazy to gun-haters but less so. For more details see Larry Coreia's argument: http://larrycorreia.wordpress.com/2012/12/20/an-opinion-on-gun-control/
I agree it should be voluntary.