[msh]

But how would you define realistic for a fantasy world?

You can't expect people to believe as they would in our world, given that their world is different. If invaders with dragons took over England in our Middle Ages and crushed the church, peoples religion would realistically also evolve very differently from what it actually did.

[the_af]

But the Targaryens behave as atheists. They don't act as if they believed the gods were judging them. Even without dragons, the subsequent kings don't act as if they were divinely ordained [1]

The vikings who massacred Christians had their own religion. What's the Targaryen's? What's the Lannisters'?

You simply cannot claim to be depicting a realistic medieval society (with magic), as Martin does, without this. And many other details he got wrong.

By Martin's own admission, dragons and magic are not an excuse for being inconsistent or "unrealistic". Vast armies cannot be raised and teleported to battlefields just because there are dragons. Dragons are no excuse for blowing up a major cathedral with no consequences.

----

[1] If you watch HBO's prequel, it's even worse: at a time when the Targaryens had plenty of dragons, there were warring factions within them, all vying for the throne, each claiming to have the "rightful" heir. But where's the legitimacy of each claim supposed to be derived from? Kings claim "rightful" inheritance through lineage, but somewhere up the line there must be a divine right to rule. So they may have disagreements about whether it's matrilineal or patrilineal (cue Henry V and the Hundred Years War), or whether someone was a bastard, but ultimately every feudal king though he had a god-given right to rule. Otherwise what would the different claimants be arguing about?