Negative campaigning has a bad reputation, routinely being disparaged as juvenile taunting that serves only to degrade public discourse.
Even devoted practitioners feel the duty to deplore negative campaigning. After commissioning an ad accusing Mitt Romney of grievous departures from conservative wisdom, Mike Huckabee was so remorseful that he refused to run it - though he managed to disseminate his charges in a news conference where he sorrowfully screened the spot for the news media. Explaining his newfound magnanimity, Mr. Huckabee asserted, "It's never too late to do the right thing."
But what was so terrible about the ad? It merely said that as governor of Massachusetts, Mr. Romney raised taxes, left a budget deficit, provided abortion coverage in his universal health care program and failed to carry out a single execution - all of which appear to be grounded in fact, and any of which a few voters would find interesting.
The spot thus passes the only two tests voters should apply to any campaign attack: Is it true, and is it important?
It would be nice if politicians were all saintly figures who invariably do the right thing. Since they are not - and since Americans often disagree on what constitutes the right thing - negative campaigning serves the helpful function of illuminating facts that a) people are likely to care about and b) the targets would prefer we didn't know.
What would we glean about the current candidates from watching only their own positive ads and presentations? That Sen. Hillary Rodham Clinton has unmatched experience in government and is a good listener. That John Edwards is tireless in fighting for you. That Mitt Romney loves his highly photogenic family. That Sen. John McCain is a common-sense conservative. That Mike Huckabee is unabashedly in favor of Christmas. That Rudolph W. Giuliani will kill terrorists with his bare hands. That Sen. Barack Obama's serene wisdom would make Gandhi look like Bill O'Reilly.
Compare those blinding revelations with what we know about the same candidates from unflattering portrayals offered by their opponents and other uncharitable souls: Mrs. Clinton's experience is greatly exaggerated. As a state senator, Mr. Obama's Zen-like approach to divisive legislation often led him to vote neither "yes" nor "no" but "present." Mr. Giuliani has a history of support for gun control and abortion rights. Mr. Huckabee has changed his position on illegal immigration. Mr. Edwards has changed his position on the Iraq war. Mr. Romney has changed his position on everything.
Any of these particular discoveries may strike you as good, bad or irrelevant. But the only reason they get attention is that they furnish some voters with information that will influence their vote.
I don't want to be entirely positive about negativity. Political attacks can also be nasty, unfair or even outrageously false. When a top Clinton campaign official wondered if Mr. Obama might have been a drug dealer in his youth, the suggestion was all three. But rather than damaging Mr. Obama, the claim backfired, forcing the aide to resign.
That episode goes to show something else good about even the most indefensible attacks: They often tell more about the attacker than the attackee. The smear of Mr. Obama reminded some people of Mrs. Clinton's pattern of ruthlessness toward her enemies.
Thomas Jefferson once said that he would prefer newspapers without a government to a government without newspapers. Given a choice between politics with no negative campaigning and politics with only negative campaigning, I suspect he would prefer the latter.
Steve Chapman is a columnist for the Chicago Tribune. His column appears Mondays and Fridays in The Sun. His e-mail is email@example.com.