Jonathan Pie explains it

[sexobon]

Even people who are fairly thick skinned with regard to name calling can get fed up when it becomes automatic demonizing. People previously called sexist automatically became rapists, people previously called anti-immigration automatically became racists, people previously called pro-gun automatically became killers. That propaganda technique works domestically when it's applied internationally and a rival country automatically becomes the evil empire; but, it backfires when applied domestically to disenfranchise segments of the population.