But wrongly rejecting good input has no security implications. But wrongly accepting bad input has.
Are you sure about that? It's arguable that it's the outcome of the action that is more important than the content or value of the action itself (i.e. By action or admission of action allow an offence to be committed).
If I have backdoored a system, and I can have the system reject good input (i.e. the sysadmin issuing a command to remove the backdoor), then the system has continued to remain insecure as a result of rejecting good input.
That may be a contrived example, but this is a topic that bears being pedantic ;) so if a principle isn't true in all cases it isn't true at all.
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For good, return good. For evil, return justice.
