That's bullshit. Admittedly, I used to think like that too. I thought that parents that do their job right will have their kids "under control". As long as you take care of them, educate them and show them right from wrong, they will all turn out all right.
Well, life showed me otherwise. I'm vastly different from my sister, even though we had the same upbringing. I know a guy who was an exemplary son until he suddenly completely broke with his parents and refuses to have contact with them, nobody knows why. His parents are great people and his sister turned out completely fine.
One of my uncles is a complete bastard whereas the rest of my aunts and uncles are great people...
There is only so much influence parents have over their children. Friends, life, the environment and their individual character also make a huge impact. Right now I'm thinking that parents can influence only about a third of a child's character. The other third is friends and environment and the rest is just pure, uncontrollable individuality.