Extremism is in the eye of the beholder
You'd be right, except that you're Right, and your definition of "extremism" is anything at all to the left of right-center. The dynamic of rejecting that kind of "extremism" only applies to the hard-core Right. Historically, mainstream Liberal positions have proven quite popular over the last half century, and it took a three-decade long Herculean effort by the Right to twist and obfuscate Liberalism, just to gain the 3% they needed to elect a Republican.
3%, David--think about how slim that margin really is, just 10% of the one-third of the electorate that's open-minded and undecided.