What is the reason why some people are liberals and others are conservatives, if it is not that liberals are more compassionate?
Fundamental differences in ideology go back to fundamental assumptions about human nature. Based on one set of assumptions, it makes perfect sense to be a liberal. Based on a different set of assumptions, it makes perfect sense to be a conservative.
The two visions are not completely symmetrical, however. For at least two centuries, the vision of the left has included a belief that those with that vision are morally superior, more caring and more compassionate.
While both sides argue that their opponents are mistaken, those on the left have declared their opponents to be not merely in error but morally flawed as well. So the idea that liberals are more caring and compassionate goes with the territory, whether or not it fits the facts.
Those on the left proclaimed their moral superiority in the 18th century and they continue to proclaim it in the 21st century. What is remarkable is how long it took for anyone to put that belief to the test -- and how completely it failed that test.
The two visions are different in another way. The vision of the left exalts the young especially as idealists while the more conservative vision warns against the narrowness and shallowness of the inexperienced. This study found young liberals to make the least charitable contributions of all, whether in money, time or blood. Idealism in words is not idealism in deeds.