I think this clause is not reasonable and should not be legal. However, these clauses (they're called "DeWitt clauses") have been around for almost 40 years and

I think this clause is not reasonable and should not be legal. However, these clauses (they're called "DeWitt clauses") have been around for almost 40 years and they have not gone away. For more, see my essay, "The DeWitt clause’s censorship should be illegal" https://dwheeler.com/essays/dewitt-clause.html https://dwheeler.com/essays/dewitt-clause.html (I mentioned it in another thread, but you might not have seen it).