This will be buried since I'm posting 12 hours after the initial post, but I find it interesting that we apply our own standards of what is moral on the world of Game of Thrones. It's a different universe. There aren't Geneva Conventions there. Think of a few things that have happened in Game of Thrones but haven't raised too many eyebrows as of late:
I'm not sure what the rules of engagement are for wars in Westeros or Essos, but I doubt there are many limitations, and if there are, few armies abide by them. When Daenerys attacked with Drogon, she killed only military personnel. I'm not saying that those unfortunate enough to not be scorched to dust instantly but instead caught on fire didn't have a miserable, excruciating, and unnecessarily painful death. I've had minor burns and I can't contemplate how painful full body burns would be, although likely that most of them would pass out from the shock shortly thereafter. But there are no agreed upon rules in the GoT universe that I know of that prohibit dragon fire on the battlefield.
It has already been said, but I didn't see as much uproar about using wildfire against Stannis' fleet, or Euron's crew cutting out people's tongues, or the mountain men brutally beating up Robb's men after the battle was won, or the flaying of men, all of which are brutal and inhumane by our standards. But that's just it, they're our standards, not theirs.
Finally, I think more people should watch Robert McNamera in The Fog of War. It's a great documentary that puts into perspective how we approached war ethics in the 20th century. I would argue that many people have forgotten how many Japanese the US killed via firebombings (500,000), which are estimated to be 3-4x as many as by the atom bombs of dropped on Nagasaki and Hiroshima. And yet the U.S. has been depicted as the good guys. We were in many ways, but we were far from perfect.
A good clip: https://www.youtube.com/watch?v=fDT8NdyoWfI