We selectively shame parents. Why do we shame them at all?

Is there a guidebook for people who are deciding whether to shame or not?
  1. Parent of 3 year old at Cincinnati zoo. Shame.
  2. Parents of Omar Mateen. No shame, yet.
  3. Affluenza Texas teen. Shame. Deserved. She was complicit.
  4. Parents of Ohio teen who shot his classmates. No shame.
  5. Parents of Stanford swimmer. Shame. Tons of it.