People acknowledge that a "sweet nothing" is a "nothing"; it has no content. So how can it be considered sweet?
Want to discuss this? Join my forum.
(Due to multi-year, sustained harassment from David Deutsch and his fans, commenting here requires an account. Accounts are not publicly available. Discussion info.)
Same way a piece of candy with no nutritive value can be considered sweet, I suppose.
Not that this vindicates the 'sweet nothing' concept all that much.
It'd be sweeter if instead of saying 'sweet nothings' they just said nothing.
Sweet nothings are not nothing. They are phatic utterances: vocalizations that have the purpose of binding people together socially or lovingly.