The difference, of course, is that in every one of those previous cases reasons had been laid out why Dany felt justified and we as an audience (usually) agreed she was justified in doing so. In this case, they didn't. They had Daenerys prioritize attacking civilians because ?
Executing the Tarlys in S7 after they had laid down their arms was not much different from this.
She executed the Tarlys because they DIDN'T. Rewatch the damn episode.
Watch it right here and tell me exactly at what point are the Tarlys holding weapons?
https://www.youtube.com/watch?v=wXGBZ1s5k9QThey and the Lannister soldiers had been disarmed at that point; they were POWs. Dany executed them because they did not want to bend the knee, ie. acknowledge her as queen. Following that logic, I suppose it would have been OK with you if she had just first asked the unarmed peasants which they preferred, her or Cersei, and then burned the ones who preferred Cersei?