Why do people have kids and end up abusing them.

I was reading a article in the paper about these parents locked their 5 year son in a closet. They starve him so bad you could see his ribs and vertebrae. Why do something like that to a kid. Why have kids if you going to end up abusing them. I really don't understand some parents. I hate reading stories   this one. Some people want kids and it hasn't happen yet. Some people do have kids and end up abusing them!!smh