Well, I've been sneaking a peek at this interesting conversation and there's a lot of excellent points made by everyone. I've had a good think about my view on this and I've added my 2c as well, for what it's worth
I don't think what is portrayed in Martin's books constitute as gratiuitous (although it is often extreme and explict!). The events which occur to these characters form part of how they view the world.
Cersei is treated, from an early age, as a political marriage dowry rather than a person. It is expected that she will become the 'perfect' wife for whoever her father may choose for her - often the very high birth nobles didn't even get a choice or say in their partner. Cersei saw this and saw her brother as being able to do the things she wished she could do. She frequently mentions how no-one could tell her & Jamie apart until she hit early puberty. How much of a shock must that have been to her?? Suddenly she's told to be pretty, learn to play the harp, learn to be obedient to her father & husband, and then there's Jamie her "twin" in every sense - they've shared everything together - now, he can become a knight, travel the land and have adventures. She's allowed none of that. Ayra is 'lucky' in some respects in that she was allowed to follow her heart and was out of the public eye, living so far north. Although, it's a matter for debate whether or not she would have been 'forced' to become more ladylike as she approached marriageable age.
Dany was shaped by her experiences too - when we first see her, she's a terrified young girl, completely dominated by her brother and yes, she is very young when she is married to Khal Drogo. I think GRRM was very brave - rather than shy away from the subject, he tackled it head on, and Dany completely changed over the course of her marriage, emotionally and physically. She was able to stand up to her brother and become a leader and "Mother of Dragons!"
Sansa was an innocent little girl with romantic dreams of being a lady - after over a year as a captive surrounded by enemies and having the sword of marrying Joffrey over her head (how glad was she when he dumped her!!??
), she was forced to grow up and grow out as a character.
I'm not trying to defend some of GRRM's depictions, but the (often horrific)events these characters go through, will greatly inform how their character changes over time. That's why I'm loving the fact that Sam, Jon, Arya, Tyrion, Sansa, Jamie, Bran et al have
all had traumatic experiences happen to them and, rather than shy away and 'spare us' the event, GRRM has allow us to crawl under the skin of these characters in a way we could never do if he "cut away" from the graphic nature of these events. I mean, c'mon, having your hands severed and then hung around your neck until they rot away? How visceral and gross an image is that - but, my goodness it certainly allowed us to understand how/why Jamie changed didn't it?
I think the, at times severe, moments in this series have turned it into one of the reasons I am able to be sucked in so completely - it may be horrifying at times, but it never feels anything less than 100% realistic.