The explanation for this strange behavior by liberals is actually fairly simple. They have very different definitions of guilt, innocence, and responsibility from conservatives'.
Liberals believe that guilt is a relative thing, because people are really not responsible for their actions. In the liberal mind, a black who grows up in a ghetto gets a free pass on being a criminal because he can't help himself. While that is obviously very racist, it's also clearly wrong, because the majority of poor blacks are not criminals.
Liberals believe that the unborn child is not innocent, but rather that she is a parasite whom the mother has the right to kill. In a liberal's mind, innocence is aligned more with the correctness of a cause than with the actions of an individual -- someone who shoots an abortionist is a monster, but the Unabomber was motivated by love of nature. Any action that furthers the liberal cause is good, so lying about Benghazi was good because it made it harder for ObamaCare to be repealed, and people who are doing what liberals think of as good are obviously, in liberal eyes, innocent of wrongdoing.
Finally, responsibility in the eyes of liberals is not a personal characteristic, but a societal one. People are not required to be responsible for their own lives, like free men have been since time immemorial; instead, it is government, guided by caring and loving liberals, which is responsible. People who don't take care of themselves are not at fault in the minds of liberals. Rather, it is society that fails by not providing a good lifestyle for those who don't want to try.
Modern liberals espouse the same "ends justifies the means" situational morality-based definitions of guilty, innocent, responsible, and irresponsible first espoused by Machiavelli and perfected by Lenin.