“Clan Mitchell,” as described in this post at Fandom_Wank, is "a shared //Stargate SG-1// alternative universe" created by IvoryGates and Dreamwidth founder Synecdochic. It centers on a huge, stereotypically close-knit Southern family presided over by matriarch “Momma Mitchell.”

A prompt was made for fic in which a Clan member brings home an SO who, though decent, does not like the Clan. The resulting fill interprets Clan Mitchell as “a highly pressurized, homogenous environment in which everyone is expected and raised to be part of the elite, where no one is normal and boring, and where there are no secrets and thus also no privacy.”

IvoryGates exploded, accusing the fill writer of “taking something that is positive and beautiful, like the Clan and its ethos, and making it something ugly… It's hateful,” and of “slurring every serving member of the military anywhere.” Synecdochic objected in a more passive-aggressive way: “But this was supposed to be a post where we opened the doors of a universe I love for people to come and create things in celebration of something I thought we were all fans of.”

While the vast majority of observers regard these reactions to making fanfic of someone else's fanfic as batshit, IvoryGates and Synecdochic definitely had equally batshit defenders:

When someone has put in a lot of blood, sweat, and tears to create an absolutely beautiful sandbox to play in (a sandbox that they love very very much), and then not only allows you to come in and play in their sandbox, but graciously opens the door and INVITES you in, you don't shit in the sandbox. You don't. M'kay? Good.

Note that Greenbirds' post attracted, shall we say, some dissenters.

Gentlefailers discuss Clan Mitchell here.