I don't personally know anyone who is like this, but I do know people in my neighborhood that I want to say plenty to for not monitoring their children as closely as they should. In the neighborhood I live in there have been 2 and 3 year old babies running around outside with no adults. I let my 4 and 5 year old go out in the yard by themselves and just down the alley 3 houses to their friends house, but my 2 and 3 year old girls DO NOT go outside without an adult with them.
On the other hand, I can see where you are coming from. The only issue is that saying something won't change what is happening anyhow. They will keep at what they are doing and alienate you from their life rather than changing anything. They will only realize what is happening when their child gets in major trouble of some kind, and possibly not even then. I know that there are parents out there who have children who have done plenty of things that they shouldn't and they always just find someone else to blame. It becomes a case of never being the fault of their baby because their baby could never do anything like that. There are times that it can even get to the point of abuse because of not doing any actual parenting when needed.