Empathy

People with higher emphathy tend to be more liberal and are less likely to support the death penalty.
http://www.tandfonline.com/doi/abs/10.1080/0735648X.2005.9721205?src=recsys

Liberals tend to have more empathy than conservatives or libertarians
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0042366#pone.0042366-Inbar2
See Table 3 - Emphathic concern row.

http://www.tandfonline.com/doi/abs/10.1300/J014v21n02_01

http://www.tandfonline.com/doi/abs/10.1080/026999300402772?src=recsys