When a public discussion of the news takes place in the news media, the viewpoints are presented by one of an ever-growing political class, the pundit. Most of the guests on Fox News, MSNBC and the like boast titles like "Republican advisor" or "Democratic strategist", meaning they've been hired at some point in their lives by some campaign somewhere. They are selected by news channels not for the depth or quality of their analysis, but by their ability to attract viewers and advertisers. This creates a perverse set of incentives for the punditry which damages the whole of political discourse and function.
There are 535 members of Congress, hundreds of Senate-confirmed positions in the Executive Branch and thousands of officeholders at the state and local level. There are millions and millions of Americans who could go online and investigate the issues themselves. And yet, most public political discourse in modern America is done by pundits. Were the pundits merely the most politically educated and articulate citizens, perhaps that wouldn't necessarily be a problem. But pundits in a world of ratings and TV news face tremendous pressure to attract attention.
To stand out from a field of countless political hacks, many pundits choose to take extreme positions, because even the most articulate argument for things like moderation and fiscal efficiency are, well, boring. So you have bomb-throwers on either side of the divide speaking for half the electorate, even though that electorate would itself be much more conciliatory since they don't have the motivation to be extreme.