I just can't look at what Daenerys did in light of her conduct in the previous seven seasons and confidently claim it was just the logical conclusion of her self-righteousness, was a conscious decision and made complete internal logical sense to her. Yes, Daenerys has always been cruel and self-righteous and probably was a villain all along. But her cruelty up to The Bells has always been deliberate; retaliation against people she thought were guilty of crimes that deserved punishment. And you might argue she just concluded the same thing about King's Landing, but that doesn't take away the fact her mind literally snapped on screen into genocidal insanity and she started indiscriminately massacring people, something she's never ever done before. She was clearly in deep psychosis and the buildup for that was just never there in the series before this year.
People keep saying she's always had madness in her and keep pointing to the things she's done throughout the series to prove it... yes, they were cruel, petty, vindictive and self-righteous. But overall, they were the same kinds of acts that have gotten Tywin Lannister or Roose Bolton a reputation of ruthlessly pragmatic. But for Daenerys, doing the same things means it's Targ madness.
We're talking about the Tywin Lannister who not only sacked King's Landing and orchestrated the Red Wedding, but whose rule literally started with, as immortalized by The Rains of Castamere, massacring an entire bloodline to the last infant and burning down their castle to the ground, in retaliation for that family not swearing fealty to him, at a younger age than Daenerys is now. He had Tyrion's wife gang-raped to punish him for dishonoring House Lannister by marrying a commoner. But I've never seen people claiming these were signs of Tywin's insanity.
Sansa looked on dispassionately, completely detached as she released Ramsay's own hounds at him, and in The Last Stark, she actually sounded nostalgic about it when she recounted it to Sandor. For Sansa, it means "[her] skin has turned to porcelain, to ivory, to steel". She's become strong and it's a sign she'll be a good ruler. Daenerys looking on dispassionately and detached as Drogo murders Viserys means it's Targ madness.