If you're saying that everyone should/must follow the law in all circumstances, that's an extreme position few people would agree with. This would mean inform on Jews to the Nazis or returning slaves to their owners under the Fugitives Slaves Act, to take an example from a democracy. That's even without considering that many laws are somewhat indeterminate, internally inconsistent or at odds with other laws.

If you're saying that there is an a priori moral presumption that laws should be followed, maybe because they represent (possibly) some sort of societal consensus, than that is a closer question, but it doesn't resolve the question of whether the legal rights of the advertisers ought to, in a moral sense, be respected.

Note though that even the US judiciary doesn't make much of a legal mandate with no penalties attached (see the last Obamacare case to reach SCOTUS).