FORTUNE — “Because he is a fake,” Republican presidential hopeful Ron Paul told CNN’s John King when asked to explain the motivation behind his attack ad slamming competitor Rick Santorum’s stance as a fiscal conservative. The audience cheered.

So it goes in America. Politicians attack each other like UFC fighters in the octagon. It didn’t matter that this was a case of Republican versus Republican, where you might assume the opponents are pulling some punches.

Both Democrats and Republicans have increasingly been resorting to negative campaigning despite clear evidence the public is fed up. A Gallup poll in late 2011 revealed historic negativity toward the U.S. government, with 82% of Americans expressing disapproval. What’s more, a growing number indicated they had little trust and confidence in the men and women holding and running for political office — 53% last year versus 32% in 2008. Many factors have polluted the politician “brand” — the weak economy, poor governance, and brutal partisanship to name a few. Another major contributor is non-stop negative marketing.

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This is a mistake businesses do not make.

When Carnival Corp.’s (CCL) Costa Concordia cruise ship sank off the coast of Italy, Royal Caribbean (RCL) didn’t start running TV ads proclaiming, “We drown less people than Carnival.” McDonalds (MCD) didn’t take out full-page newspaper ads saying, “No E. coli here” in 1993 when bacteria-tainted burgers from Jack in the Box were killing people. And Dominos (DPZ) will never resort to messages such as, “Our pizza won’t make you as fat as Papa John’s (PZZA).”

The reason you never see this type of marketing is because of an unwritten rule in business that says, “don’t destroy the category.”

Companies do attack each other, but they walk a very fine line. They are careful not to kill the goose that lays the golden egg. Before people will buy Ben & Jerry’s ice cream, they have to like ice cream. That means while Häagen-Dazs and Ben & Jerry’s brands may duke it out in the supermarket aisle, they will avoid any message that might make us stop eating ice cream. These competitors share the common goal of wanting to expand the ice cream category. Thus, any attack on each other must not undermine the more important goal of growing the overall market.

Politicians don’t understand this. Clearly, many of them and their marketing consultants swear by the attack strategy. And they don’t stop at attacking each other. They routinely bash the entire opposing party and Washington, D.C., itself with messages such as, “Washington is broken, blah, blah.” They heap negativity on top of negativity.

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For decades, the American public has heard politicians call each other dirt bags. The Gallup data proves that marketing strategy is working. The mantra has been so effective that many Americans now believe all politicians must be scum. Politicians have committed the biggest marketing sin of all. They have destroyed their own market category.

In spite of this revelation, don’t expect much to change. Politicians believe attack marketing is effective for winning offices and seats in the short term, in spite of the fact that the practice undermines the credibility of our democracy in the long term. They could learn something from big corporations.

Christopher Lochhead is a former Chief Marketing Officer, and co-founder and partner with Play Bigger Advisors. Twitter: @playbiggeradv