This article
summarizes the various arguments about Dany's decision, citing some thoughtful reviews. Worth a read, IMO. I found the section on whether Dany is actually mad or instead ruthless and rationale particularly compelling because I don't believe its a POV covered in thread.
I'm still firmly in the camp "her decision was unearned". There is plenty of show evidence that Dany is ruthless (against enemies), revenge-seeking, righteous, messianic, increasingly paranoid, feeling spurned by her dumba** nephew, etc. It's all been cited in this thread. None of it contravenes what the show presents as a core Dany purpose --- a desire to break chains, help people, and free the enslaved. We're hit over the head with it over and over. This belief and willingness to sacrifice herself for it is why Tyrion, Varys (for a bit), Jorah, Selmy, Grey Worm, Missandei, etc became so loyal. They thought she was different because her actions were different from any of the other kings and queens they (or we) had seen.
Look, I believe GRRM's intent is for Dany to become the mad queen. The structure of his books --- with each chapter devoted to a character POV --- offers a whole heck of a lot more insight into what characters think. But for show viewers, in S8E3 we see Dany sacrifice herself and her army to save humanity then are expected to pivot to Dany not "descending into madness" as her father did, but cannonball-ing into it with a hurried killing of Rhaegal and Missandei in between. So we go from saves all the people to kills all the people in 1 episode. Meanwhile, Stannis Baratheon gets four seasons for us to see him slowly sacrifice everything in the name of the throne...