Now if he was going to launch BASEBALLS that would be dangerous.
This shows the idiotic nature of political correctness. It is not the danger posed by a thing but the symbolic value of the object.
A tennis ball launched by a trebuchet has nearly zero chance of harming anyone, but because the tennis ball launched by a trebuchet symbolizes a missile used as a weapon of war it must not be permitted to pollute the minds of our impressionable youth.
It looks like your son did an excellent job by the way.