What is wrong with people?

Every time I read something like this (and it happens way too often), I get sick to my stomach.
How can people treat their own children like they have no feelings and aren't worth anything?

BOYNTON BEACH - A woman and her boyfriend used a bedsheet to tie up her 1-year-old daughter so they could go out dancing, according to police.

The baby's grandmother, Olivia Claros, 50, arrived home shortly after 10 p.m. Saturday and heard her granddaughter, Hayli Nicole Claros, crying hysterically from a bedroom. A sheet was tied around her neck, arms and legs, according to a police report.

via the Drudge Report