I would LOVE to know what a Thomist would say here. Anybody out there who knows St. Thomas’ works well?
Summa, Prima Secundae Partis, 96.6: *Wherefore if a case arise wherein the observance of that law would be hurtful to the general welfare, it should not be observed. For instance, suppose that in a besieged city it be an established law that the gates of the city are to be kept closed, this is good for public welfare as a general rule: but, it were to happen that the enemy are in pursuit of certain citizens, who are defenders of the city, it would be a great loss to the city, if the gates were not opened to them: and so in that case the gates ought to be opened, contrary to the letter of the law, in order to maintain the common weal, which the lawgiver had in view.
Nevertheless it must be noted, that if the observance of the law according to the letter does not involve any sudden risk needing instant remedy, it is not competent for everyone to expound what is useful and what is not useful to the state: those alone can do this who are in authority, and who, on account of such like cases, have the power to dispense from the laws. If, however, the peril be so sudden as not to allow of the delay involved by referring the matter to authority, the mere necessity brings with it a dispensation, since necessity knows no law.*
To summarize, don’t break the law (in this case, against vandalism) since it’s
just a poster and isn’t causing any immediate peril.