This may not be the flavor of defensive programming you favor, but it is something that exists, and also something that is explicitly mentioned in the start of the discussion.
It counts for something, but yours does not count more than anyone else's - and it is certainly not sufficient to make a general case against validation. Pointing out that bad or incorrect validation is bad is news to no-one, and is merely a specific case of bad code being harmful.
>...something that is explicitly mentioned in the start of the discussion.
As for your anecdotal evidence, it does not count twice through repetition.