Bill:  Interesting premise.... However, it's not always the case that concomitance implies causality.  Yesterday I wore new socks and last night it rained.  That certainly doesn't mean my wearing new socks caused it to rain.  Additionally, of course, we might consider "cause and effect."  Liberalism, for example, has emerged and flourished in reaction to difficult times;  the Abolitionish Movement in reaction to slavery; the Progressive Movement in reaction to The Guilded Age; and FDR liberal thought and action in reaction to the Depression.  I would suggest that advances in liberal thought are reactions to the many problems of our nation's history over the last fifty plus years...racial, gender and class inequalities leading the way.  

In my face to face (and on this site) interactions the most civil individuals I've met have tended to be liberals.....the least civil have been"far-right-wingers..and, yes, there are a few angry, uncivil individuals on the left as well.  Gary Crum