Airhead, some would consider political presentations to be inappropriate in public....period. I would also point out that if Code Pink had been invited to speak in a public school, and then the administration denied them the right to speak because of parental protests, we would be having an entirely DIFFERENT discussion right now.
These veterans have been speaking in public places and in schools all over the country, and as far as I can determine, there have been no inappropriate actions on their part. If we follow your line of reasoning on this subject, then we should refrain from inviting any government official, soldier, diplomat, mayor, judge, fireman, minister, or atheist to speak in our schools for fear that they "might" make a political statement.
Soldiers have been speaking in our schools for about two centuries. That it has only now been seen as inappropriate comments negatively about our "modern" values.