I might expand in the case of threesome because I'm amazed at the number of people who think that HGSSLM will not include LMSS touching because zomg that's just not the way it's done in porn films.

I don't like suprise pairings myself. I have sympathy with that.

Conversely I get fed up with warnings for het, but that's just personal aggravation rather than a moral principle. It's not the same, not the same thing at all.