A popular tactic in politics is to put the voters off the other candidate. Many choices become a matter of choosing between the lesser of two evils. As a presidential candidate it's about making the other candidate seem so repulsive to the voter that they end up opting for you not because they like you, but because they couldn't bear the thought of seeing your opponent win.
In the ideal world it would be all about showing what you as a candidate have to offer and from there let the people decide; but in reality we the voters want to know the bad about our candidates too, often more than we want to know about the good.
As much as many people say they don't care about attack ads, there's an element inside us that wants to see the dirt each candidate has on the other. The run-up to the U.S. elections is like a six month long mudslinging contest that the public watch unfolding; and the candidate who doesn't smear the other only ends up covered in mud while his counterpart's image remains clean come election day. Smearing your opponent is as important as painting a good picture of yourself. In modern politics, especially in America, smearing is unfortunately essential, as un-idealistic as it may be.
"It was like building my own coffin," says the ex-factory employee in the clip below. This video details one of Mitt Romney's alleged corporate raids where he buys a factory, shuts the operation down and sells the assets off. This is just a normal citizen appearing to sincerely express his disgust at Barack Obama's opponent. It is an attack ad with context, because it's being presented by someone that most citizens can relate to, and he looks very convincing to boot. Irrespective of who Americans pick between Obama and Romney, this ad makes impact, and is a prime example of why attack ads are used.