The problem is that is how she was played in the series. Ruthless against her enemies, yes, but always a defender of the innocent. Never even a hint that she might kill babies?
Seriously, though, Dany fans on Westeros.org are beside themselves trying to defend her, criticise the writing and say ‘George wouldn’t do that’. They are trying to psychoanalyse her and look for imaginary mental health conditions or lack thereof or imaginary scenarios where what she does is ‘less evil’ but has the same consequences.
Yes, the writing and character development has been less than good - but nobody was screaming about this in season 6 and 7 when it was ‘evil Sansa’ being badly written. She was always ‘destined’ to be stupid and manipulative right?
I seriously doubt that anything other than this is going to go down in the books. She is going to destroy Kings Landing along with most of its population. Whichever way you cut it, there is going to be no ‘good’ ending for her.
As far as psychoanalysis and George’s ‘expertise’ in it goes - his scientific knowledge is somewhat flaky on many subjects. Many of his characters have prophetic dreams and visions. As far as I know, this doesn’t fall into any current recognised field of psychoanalysis. His understanding and use of genetics, inheritance and medical conditions is imaginative and clearly fantastical.
People like to claim that his universe has ‘rules’, but they cannot be directly compared to ours in any branch of science.
That dragon would have run out of flame power on the first breath, for one.