Game Of Thrones: How Daenerys Became The Mad Queen (And Why The Hate Is Wrong)
6. "A Targaryen Alone...."

The strangest part of the whole Dany discussion has been the suggestion that there simply wasn't enough of a trigger for her to lose her mind and start killing innocents. That her sudden hair-trigger "change" into an innocent-killing monster was conjured out of thin air.
Even putting aside the hints from elsewhere in the show, to misread that is astonishing. For all of her links to the supernatural, Dany is human. She is vulnerable and emotional and weak in the same terms as everyone else in the show and the expectation that she could somehow not react to her condition at the start of the penultimate episode in a similar way to Cersei destroying the Sept of Baelor is incredibly unfair.
The trigger was not instant: for the whole of this season, since Jon told her about the true secret of his parentage, Dany has seen her support system needled away. That immediately drove a wedge between her and the Starks (even if she ignored it somewhat with Jon because of their love), which was compounded by the frosty reception the Northerners gave her as an outsider. As she told Jon last episode, there is no love for her in Westeros.
Compare that with the adulation she received as a liberator of other lands - to almost deifying levels, in fact - and you can begin to understand why she might not have as close a bond with the people. Yes, she freed slaves and protected innocents, but they were grateful, they wanted it, they didn't see her as an enemy. But still, that alone isn't enough.
You then have to consider the systematic destruction of her inner circle. Jon's bond was insidiously compromised by the secret of his blood, and then in quick succession, Dany learned of betrayals by Tyrion and Varys (one of whom plotted to poison her), which followed a devastating period in which she lost Viserion, Jorah, Rhaegal and Missandei. All of her true relationships AND her political ones were broken apart. She was, at this point, a Targaryen alone faced with "liberating" a people who saw her as a monster and who had, in her eyes, sanctioned the murder of Missandei.
Consider the reaction to Dany killing the Tarlys: she was accused of being an unjust monster once more, unable to arrest her emotions in the name of regal justice. She became the villain, despite them refusing to kneel to her having been hell-bent on killing her. So she killed them. When Cersei did the same thing with someone (Missandei) who wasn't even a combatant, there was no flicker from her people. She's human, that would hurt.
And to go back to what Maestor Aemon said: "a Targaryen alone in the world is a terrible thing." Even worse, a Targaryen alone believing herself attacked on all sides is an even worse one.
[Simon]