Of course it is. But no matter how I read that sentence, I cannot parse something someone of your calibre could possibly have meant.

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 You most probably didn't mean that input validation is superseded by some other technique, and therefore best ignored.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?