We Only See the World as Black-and-White When We Are Afraid.

When people are afraid, they tend to see their problems in black-and-white terms.  They tend to block out contrasting information, and want a muscular solution.  These are the characteristics that lead to authoritarianism, which we are all prone to sometimes.

I often hear laments about the polarization and partisanship that comes from people - other people - being closed-minded, narrow-minded, or, again, seeing things only in black and white. 

As I review the psychological studies I know and the anecdotes I can think of, I have a hunch:  we only see the world in black-and-white terms when we are fearful.  When we are reasoning calmly, everyone is able to see positions in the middle.