In my opinion calling content contributed in good faith by our valued contributors "cruft" is incivil. It sends the clear message that their contributions, and by extension themselves, are valueless.
Reductio ad absurdum time:
"In my opinion, nominating content contributed by our valued contributors is incivil. It sends the clear message that their contributions, and by extension themselves, are valueless."
Nothing absurd about it, deleting someone's contributions DOES send the signal that that particular contribution is considered valueless by the deleting authority (speedying admin or supermajority of AfD folks).
You missed two important points there:
1. "and, by extension, themselves" 2. Kelly's' implied conclusion is that we shouldn't call things "cruft". By her reasoning, we should never delete anything either.