Why do some parents refuse to take responsibility for their childrens upbringing?

I am baffled and disgusted by the attitudes some parents have regarding their child's poor upbringing, they love to blame teachers, affirmative action, laws, McDonald's etc, basically anyone but themselves. I am tired of hearing parents whine about their child's lack of opportunities after they allowed their children pull straight d's in school, har their clmates and smoke pot, rely on happy meals for dinner every night, and generally not give a flying f*ck about their child's actions. Then they turn around and blame affirmative action, asians, and jews for "stealing" their child's spot in the ivy leagues, blame teachers for not raising their child properly while they were in high school, blame racism for their children's incarceration after selling drugs, blame lack of health care and McDonald's for their child's weight problems, and blame mexicans for stealing all of the wonderful crop-picking jobs from their children. WTF is wrong with some people? Why can't they realize their child's lack of success is because of their failures as a parent and their child's failures as an adult?