The school has no power to tell students that they cannot engage in whatever legal behavior they want outside of school grounds.
Of course they can. All they have to do is pass a rule, like the ones you claim are just fine on other issues.
The board is elected by the people and they can usurp any rights they wish by making the rules. If you don't like it they will come after you with a court order.
You really do need to get consistent in your posting.