Political discussion is generally of three types: analysis, philosophy, and advocacy. We discuss events and their impact on electoral races, as if they're sporting events. We talk about the proper role of government. And, we promote issues and candidates. Unfortunately, the line between philosophy and advocacy is blurred, because what we want done follows from what we believe is right.
But neither political philosophy nor advocacy is purely intellectual. Justice isn't defined so much as felt. When our sense of justice is attacked, we do not react by saying, "What a fascinating proposition! I will analyze this and after careful thought decide if this is logical and true." Instead, we fight back. And we must. Politics is war, in the sense that politics determines who controls the land. It is natural to want the people in charge to be in line with our own values.
That is why I am not bothered by the ad hominem attack in political debate. It is an oft-used, but also much-maligned, rhetorical tactic. Charging someone with making ad hominem attacks implies that this person is coarsening civil discourse and helping to wreck civilization. Ad hominem means "against the person." It is the logical fallacy that the truth of a claim depends on the qualities, virtues, or circumstances of the person making the claim. An example: "Jack says '2+2=4,' but Jack is a jerk, Jack's been wrong lots of times before, and Jack is a paid shill of the Mathematics Establishment, so we shouldn't listen to Jack."
We know that 2+2=4, even though we might not like Jack. But we can not apply this lesson to politics. There is usually less objectivity, and far more subjectivity, in factual claims than we care to admit. For the ad hominem is but the inverse of another logical fallacy, the argument from authority. After all, just because Einstein says 2+2=4, does not make it true, any more than an untrustworthy source saying it would make it false. In the real world, however, we get by not on logic, but on trust. We do not have the time to investigate and figure out everything ourselves. We must rely on others, and must choose on whom to rely. We can't help but rely on those who share our values.
The undercurrent beneath the condemnation of ad hominems is the assumption that everyone means well, and everyone's views deserve a fair hearing. The expectation, then, is that we be polite and "agree to disagree." One problem with this is, people are free to express opinions that promote violence and intolerance, such as war or censorship, but in the interest of "civility" others are not free to call them out for these most uncivil positions. Another problem is that everyone advocates policies they think will make the world a better place. Everyone "means well." Everyone, from their own perspective, has "good intentions." Including Osama bin Laden. That does mean it is possible to reason with them.
A third problem is that politics does not depend on logic, but on persuasion. In the long run we are not persuaded just through our rational minds, but by what "feels" right. Debate is about persuading the audience, not the opponent. And associating the opponent with abhorrent beliefs and practices can potentially persuade the audience And if the audience is already on your side, demonizing the enemy in front of them can enthuse and rally them all the more. The ad hominem attack is no more unfair or uncivil than any other logically fallacious rhetorical tactic, precisely because the charges often do stick. If the Congressman receives campaign contributions from defense contractors, how can we trust him when he says our national security depends on spending more on the military? He may even be right, but it is more than fair for his opponent to point out this relationship. Also, other fallacious rhetorical devices often get free reign. Politicians like to throw around words like "compassion" and "for the children" all the time, not to change our minds, but to arouse our passions and confirm our prejudices in favor of more government. Why is this acceptable, but ad hominems are not?
The final problem with condemning ad hominems is that they provide a good place to draw a line in the sand. The ad hominem shouldn't replace valid arguments, because that is a sign of weakness. But still, it is good to use it as a first resort, as an expression of what is simply not acceptable. "I think we need an open, honest debate about the benefits of incest and pedophilia." Uh, no. To play nice, to even engage in the debate, is to grant it some legitimacy. It would be a small victory for the other side. They have their "in." The better response would be, "Get the hell out of here, you creep. Do the world a favor and jump off a bridge."
In discussing political philosophy, it is best to remain and civil and patient as possible, offering up different viewpoints with respect and empathy. When it comes to political advocacy, however, the gloves often have to come off. It is one thing to discuss in the abstract whether the state has the right to ban smoking. But when it comes to advocacy, the defense of liberty may require gouging the eyes, kicking the groin, or whatever it takes to keep those sanctimonious tobacco Nazis off our freaking backs.
Ad hominems may not be the best weapon. They are best used sparingly, preferably but not always when "they started it." The purpose in using them should be persuasion, not just to vent anger. But ultimately, all's fair in politics, particularly when our opponents stand for war, repression, and economic enslavement. It is acceptable to kill in self-defense; why is it unacceptable to call somebody names in self-defense?