All citizens have certain rights, as expressed and/or implied in the constitution, and with those rights come responsibilities. These responsibilities must be fulfilled in order to gain access to these rights. Specifically, while citizens have the right to free speech, and thereby the right to freely express their opinion, they have a responsibility to respect others and defend the constitution, among other responsibilities, which Donald Trump has failed to do.
Of course, citizens are absolutely allowed to express disapproval in their country--it comes with the right to free speech. But, in doing so, it is not fair to the country, and its citizens, to damage its reputation.
Trump is damaging our international reputation and this mockery must stop before the damage becomes irreparable.