I'll be honest I've not seen the first two series so I'll avoid speculating. I'm sure you are absolutely right.
In the case of Game of Thrones, a lot of the more 'liberal' sexual encounters were really put in for shock value or an excuse for nudity, for example Oberyn's orgy scenes. I never really got the feeling it was trying to normalise these things, but that was just my interpretation.
Similarly for Friends my interpretation was characters like Joey were to be the punchline of a joke, not to say his behaviour was normal. It felt more to laugh AT him, not to normalise it.
My experiences of mainstream media seems to largely focus on the young bachelor(ette) who has casual sex as a 'phase', or the monogamous faithful couple who've grown up and matured. Despite this narrative, I really don't believe monogamy works for a fair percentage of the population. This leads to either two states:-
1. They never form close romantic relationships, leading to more casual sex and probably larger risk of spreading STDs.
2. They do engage in a monogamous relationship, only for it to turn sour because of the tensions it causes. In some cases this leads to a party cheating on the other. These people almost never go to STI clinics to get tested for fear it will ruin their relationships.
How about instead the mainstream media embraced the idea of wanting to have multiple sexual partners is fine regardless of your stage of your life or your relationship status? That way, we can have make sure that everyone is informed of the risks and getting the medical treatment they need to keep themselves and others safe (particularly regular testing). As soon as you start demonising it and saying you shouldn't feel that way, people will do it anyway and just hide it instead.