Two words: Umair Haque.

More to the point, though - anger is a highly arousing emotion and gets a lot of clicks. Research on viral content has shown, for example, that headlines that evoke anger are more likely to gain traction and lots of reads - and this was from a study conducted using the New York Times' website. Anger was one of the strongest drivers of attention (though there were others that were close).

Also, hatred for an outgroup fosters a sense of community (I spent a lot of time studying this as a social psychologist).

There are a thousand reasons why anger works.

The question isn't whether it brings in clicks. The real question is the cost. When faced with the question of how to get attention online a lot of people appeal to anger because it's a cheap fix to their problem - but like most cheap fixes it has hidden costs.