The trouble with that is that the old tweets from an immature brain are amplified beyond their original context, intentionally, so that they hurt a lot of people, and then a punishment is applied as if the author had just deliberately blasted the world with their remark yesterday. People are using the private conversation analogy because so many teens just meant to write to a few friends or use it as a sort of diary. To make them responsible not only for their youthful immaturity their whole life, but for any mental health struggles, and for not having a perfect understanding of the nature of the service, is cruel and non-productive social behavior from the adults.

You’re having trouble understanding because you are only imagining yourself making these decisions, and you are a fully grown adult who handles life’s pressures well and you understand Twitter from a product perspective. You will need to consider how others use the service to understand why expecting perfect behavior across every person’s entire life is unwise collective behavior.