Liberal smugness is a bad idea - especially for liberals. But there are several other factors that have produced a very evil political climate in the US today, and liberals had almost nothing to do with them.
One generator of lousy and contentious US politics is a 60-year campaign by rich, super rightwing business leaders and libertarian extremists to undermine the basically humane and economically helpful New Deal legislation of the 1930s. See historian Kim Phillips-Fein's book on this: "Invisible Hands: The Businessman's Crusade Against the New Deal" for details.
2. A second generator of nasty, brutal politics in the US today is a decade-long campaign by KKK-style white racists to make racial hatred common and to roll back the reforms of the Civil Rights movement. See "Dog-Whistle Politics," by Ian Haney Lopez, for details on how this has worked since the Nixon White House adopted its "southern strategy" in about 1972.
3. A third generator of anger and hate in US politics is the huge surge of immigration, legal and otherwise, that's occurred in the US since the 1970s. Historically, an angry "nativist" backlash has followed every big wave of immigration in US history, and this time is no exception.
4. A fourth big generator of conflict & hatred in US politics is the growing inequality in this country between the super-wealthy and almost everybody else. We now have what some writers call "Winner-Take-All Economics" in the capitalist marketplace, plus what other writers call "Winner-Take-All Politics" in the halls of government, and many people hate it and are upset by it.
5. We're also seeing technological, cultural and economic changes on steroids in our society. Capitalism has always depended on the "revolutionizing" of technology and almost everything that goes with it, but the disruption this causes has become much, much worse since around 1950.
This means many, many people end up suffering from "Future Shock," as Alvin Toffler wrote in around 1974. And what "Future Shock" produces is what Ronald (?) Barber has called the fight of "Jihad vs. McWorld," where more culturally conservative people flock to fundamentalist, sometimes violent religions as a refuge against what looks to them like a crazily secular world, even as more secular and modernist-friendly people flock to the big cities to fight against the cultural fundamentalists.
Liberal smugness is a reaction to some of these forces. I don't think it's a major cause of them. Also, "liberal smugness" is partly a nasty meme that rightwing business conservatives and would-be fascists have made up to demonize liberals, so that the demonizers can push a rightwing agenda.
-- democratic socialist