Sanders campaign has become a classic example of the phenomenon of "group polarization"

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165. There is value in group polarization

That's how dedicated partisans who will give their all to a cause are made. Bernie sparked more group polarization than any other candidate for the Democrats in a long time, with strong ideological stands. That is good for the Democratic party as it has essentially become a least common denominator party, trying to appeal to a very diverse set of voters, from moderate conservatives to ultra liberals. The downside is that Bernie's most adamant supporters will not support the Party's standard bearer for President, because she has been demonized as a non-believer/non-ideologue pragmatist.

Demonization of the opposition is a common element of group polarization and is often based on appeals to moral superiority. But this effect goes way beyond Bernie among political partisans. The tea party demonizes Democrats. Progressives demonize Republicans, etc. DU itself is the perfect breeding ground for group polarization where members try to out "progressive" each other. But in all cases, this motivates people to get things done.