moderated Re: delete old messages
Disagree. Are you saying you can provide an example showing it's practical?
I simply said that the Yahoo TOS (pre-Verizon, anyway) provides example text that limits the license granted to the service. That limitation means that if the member (or Yahoo) removes their content then Yahoo would no longer have the right to display it. Yahoo treated that language as requiring that members be able to remove their content.
You'd have to be able to guarantee users that at any point in time, they could request their content be removed from any and all groups, regardless of whether they'd left any or all of those groups or even groups.io as a whole, whether a week, a month, or a decade later. I think that's pretty clearly impractical.
Yahoo did not find it to be impractical. I know of cases where Customer Care intervened to require that members be allowed back into groups in order to delete their messages, and also cases where Customer Care did the deletion on behalf of the former member if the group managers refused or were unresponsive.