If the picture of the gun is the problem...would he have been suspended if the same gun was on his shirt, but it said..."Ban Assault Weapons" instead of "Protect Your Rights"?
There is nothing on his shirt that is offensive. There is nothing on his shirt that promotes terrorism, violence, mass shootings, etc. Expressing support for an Amendment in the Constitution of the United States is not against any rules of the school
The school was wrong, plain and simple.