That's a silly way to read what I said.
Unless I missed something, you couldn't have meant that input validation is useless. You most probably didn't mean that input validation is superseded by some other technique, and therefore best ignored. You couldn't possibly think that everyone already does input validation, and therefore don't need the advice.
But then I wonder. Why saying "validate all your inputs" is not useful? What would you say instead?
Besides, it's not just about us: other people, (including @carty76ers apparently) would like to know what you would advise instead of "please validate all inputs".
The reason I kept guessing, was because you kept not telling. Until then: https://news.ycombinator.com/item?id=21719065
Finally something I can argue with.