Isn't it obvious? These parents could be on drugs, have a mental disorder, anger management isssues, or even a booze problem. For a parent to kill there child something must be distorting their rational thinking. So, if their rational thinking is distorted, how can you expect them to rationalize that there are parents out there who can't have kids who would love kids? When they commit the crime they, I would imagine, don't know what they are doing or are so enraged they don't care. Not saying those reasons are excuses or justifications, but they are explanations to an extent.
-Keennan
http://www.teachmechess.com