If the evidence were undeniable would that be cause to ban social media for the youth?

We cannot simply ban things if they are bad, however weak or strong the evidence is. We have to examine access on the basis of rights alone. If the right exists then it could kill all kids and it would still be the correct decision to allow it.

What is being modified _is_ the right. Examining the right is not the point here. Unless you mean something else than the law?