Secret alts themselves are WAY bigger theoretical problem than forum mods having knowledge of secret alts.
People play differently when I'm in a game. If I wanted to gain an unfair advantage, I'd play under a secret alt and have a distinct advantage over players who don't know they have to play around Glork.
I sort of kind of get what LLD is saying, but I feel as though she's missing the forest for the trees if she wants to discuss the fairness of (secret) alts in mafia games.