In respect of the incident where a gunman ambushed Republican lawmakers during baseball practice at a Virginia field, injuring four people, Fox News host Sean Hannity has laid the blame on Democrats, arguing the left had "de-humanised" Republicans and painted them as "monsters".
This is a grossly hypocritical remark and an attempt to make political capital out of an act of hatred that should be regarded as an attack on humanity. However, he does have a point. Leftwing people do paint their opponents as either evil or stupid (or, in the case of Donald Trump, both). This is a great sin of ours and one that seems to always backfire. Nobody is going to listen to the arguments of people who are calling them thick and nasty no matter how sensible the arguments happen to be.
My guess is that this belittling of the opposition is a product of another bad trait of ours, our arrogance. We are shocked when things do not go our way because we just cannot believe that the "common herd" would choose not to think and do exactly what we, their intellectual and moral superiors, tell them to think and do.
A substantial dose of humility and self-examination and a whole lot of attempting to understand those who have different values to us would not do us on the left any harm whatsoever. In fact, it would probably be to our advantage in the long run. It could not possibly be more harmful to our cause than our current belligerency and our constant resorting to childish name-calling.