Yeah, a blanket warning would not be helpful at all for me. And on fannish archives that is actually not how it is implemented either. Journals neither. I mean, archives warn usually you for every story separately (like the javascript boxes you have to click through on eFiction archives), and on journal sites you see adult flags and the like entry specific. You can disable the warnings on some sites, but I do not just get a single warning here on DW for example, but labels on every entry the owner marked.