I do not believe that the Ancients themselves are to blame for the destruction that befell them. From what we saw of their society it was a very peaceful one. The use of creation magic was also regulated and not simply used for pure decadence. In addition, debate was encouraged and decisions were weighed carefully. We also see the sheer scale of the destruction wrought upon the Ancients in the Amaurot dungeon itself. Bringing forth Zodiark was not done on a whim, it was very much presented as a necessity to prevent the Star from fading into nothing.

Having the blame pinned on the Ancients would be a pretty disappointing revelation and I do not doubt that the only reason it is pushed so heavily as a theory around these parts is due to the resident Hydaelyn enthusiasts desperately wanting her to be free of any and all blame, no matter how many characters or factions have to be thrown under the bus in order for such to occur.