It's not as front-and-center in his letters as it used to be - for Yuletide 2020, he DNWed "non-canon relationships", which wouldn't make most people bat an eye. (Still sort of hilarious, coming from him: non-canonical dewclaws, sure, but relationships, why, that's a bridge too far!)
But if you move backward to some of his older letters, he DNWs non-canonical relationships and then also includes commentary like "slash make[s] me twitch spasmodically", or "I'm also not terribly fond of slash, unless it's canon for the characters involved to swing that way. In my opinion, the best way to avoid these things is to remain true to the characters, which fortunately also has the effect of making for better stories." (Which, again, being lectured by Untherius about how slash isn't "true" to the characters, and sticking close to canon makes for better fic, is quite something.)
Re: Untherius?
It's not as front-and-center in his letters as it used to be - for Yuletide 2020, he DNWed "non-canon relationships", which wouldn't make most people bat an eye. (Still sort of hilarious, coming from him: non-canonical dewclaws, sure, but relationships, why, that's a bridge too far!)
But if you move backward to some of his older letters, he DNWs non-canonical relationships and then also includes commentary like "slash make[s] me twitch spasmodically", or "I'm also not terribly fond of slash, unless it's canon for the characters involved to swing that way. In my opinion, the best way to avoid these things is to remain true to the characters, which fortunately also has the effect of making for better stories." (Which, again, being lectured by Untherius about how slash isn't "true" to the characters, and sticking close to canon makes for better fic, is quite something.)