[Tiberius] was, moreover, quite unperturbed by abuse, slander, or lampoons on himself and his family, and would often say that liberty to speak and think as one pleases is the test of a free country. When the Senate asked that those who had offended in this way should be brought to book, he replied: 'We cannot spare the time to undertake any such new enterprise. Open that window, and you will let in such a rush of denunciations as to waste your whole working day; everyone will take this opportunity of airing some private feud.'
Though Tiberius is infamous for his depravities, he seems remarkably pragmatic in this situation. Just as modern politicians need to be thick-skinned when it comes to public criticism, so too did ancient Roman public figures. There's a certain amount of futility in trying to punish every single bad comment that is directed at politicians, and that amount is a whole truckload. Besides, if you were to try to chase down all of the sneers and jeers against you (assuming you are a politician) you would be so occupied with this endeavor that you would get bogged down and have absolutely no time for the job that your constituents elected you to do. Tiberius recognized that, sick creep that he was.
Tiberius also raises the idea of free speech and freedom of expression (though only for Roman citizens, I'm sure) as an example of a good thing for a thriving society, and we here in the United States are certainly no strangers to this concept. He welcomed criticism, and we can only hope that our modern political types would follow his example.
Imagine that: Me, the paragon of free speech! Who'd a thunk it?