I see your argument and it's a strong one, I merely haven't considered the issue deeply enough to have much confidence that there aren't other strong arguments

I see your argument and it's a strong one, I merely haven't considered the issue deeply enough to have much confidence that there aren't other strong arguments the other way. I don't object to your making the claim, I merely wouldn't make it myself :) That said, I think the fact that there's a hard question here stems from SQL's conflation of "I don't know this" with "this is known to be absent". If NULL always represented the latter, implicitly omitting them from aggregates would be clearly correct.