>> Youtube incident in 2008.
I see a distinction between policy and authorization.
Policy is something the ISP decides for themselves - "I make my own routing policy as to what is my best path".
BGP was created to make it possible for operators to have that policy decision.
There are those who call route leaks an authorization problem.  [[[I think.]]]]  They want to be able to say "I authorize my neighbor to propagate this announcement with the following constraints (no peers, no transit, customers only, etc)."  [[[I think.]]]  Again, operators could decide to enforce that authorization in their policy or not, but those wanting to stop route leaks want to make the determination of what is authorized.