A new reader (who may not remain a reader for long) wrote in to say that he enjoyed my philosophical entries but was "saddened" by the invective I employed in one of my political posts.
I would say that the use of invective is justifiable in polemical writing. Of course, it is out of place in strictly philosophical writing and discussion, but that is because philosophy is inquiry into the truth, not defense of what one antecedently takes to be the truth. When philosophy becomes polemical, it ceases to be philosophy. Philosophy as it is actually practiced, however, is often degenerate and falls short of this ideal. But the ideal is a genuine and realizable one. We know that it is realizable because we know of cases when it has been realized. By contrast, political discourse either cannot fail to be polemical or is normally polemical.
Let me then hazard the following stark formulation, one that admittedly requires more thought and may need qualification. When philosophy becomes polemical, it ceases to be philosophy. But when political discourse ceases to be polemical, it ceases to be political discourse.
A bold pronunciamento, not in its first limb, but in its second. The second limb is true if the Converse Clausewitz Principle is true: Politics is war conducted by other means. Whether the CCP is true is a tough nut that I won't bite into just yet. But it certainly seems to be true as a matter of fact. Whether it must be true is a further question.
Another possible support for the second limb is the thought that man, contrary to what Aristotle famously said, is not by nature zoon politikon, a political animal. No doubt man is by nature a social animal. But there is no necessity in rerum natura that there be a polis, a state. It is arguably not natural there be a state. The state is a necessary evil given our highly imperfect condition. We need it, but we would be better off without it, given its coercive nature, if we could get on without it. But we can't get on without it given our fallen nature. So it is a necessary evil: it's bad that we need it, but (instrumentally) good that we have it given that we need it.
Of course my bold (and bolded) statement needs qualification. Here is a counterexample to the second limb. Two people are discussing a political question. They agree with each other in the main and are merely reinforicing each other and refining the formulation of their common position. That is political discourse, but it is not polemical. So I need to make a distinction between 'wide' and 'narrow' political discourse. Work for later.
Now for a concrete example of an issue in which polemic and the use of invective is justified.
Can one reasonably maintain that the photo ID requirement at polling places 'disenfrachises' blacks and other minorities as hordes of liberals maintain? No, one cannot. To maintain such a thing is to remove oneself from the company of the reasonable. It is not enough to calmly present one's argument on a question like this. One must give them, but one must do more since it is not merely a theoretical question. It is a crucially important practical question and it is important that the correct view prevail. If our benighted opponents cannot see that they are wrong, if they are not persuaded by our careful arguments, then they must be countered in other ways. Mockery, derision, and the impugning of motives become appropriate weapons. If you don't have a logical leg to stand on, then it becomes legitimate for me to call into question your motives and to ascribe unsavory ones to you. For, though you lack reasons for your views, you have plenty of motives; and because the position you maintain is deleterious, your motives must be unsavory or outright evil, assuming you are not just plain stupid.
Companion post: The Enmity Potential of Thought and Philosophy as Blood Sport