I dont think its the concept of good, which he is blaming.
"So this is the end," Tanis said. "Good has triumphed.
"Good? Triumph?" Fizban repeated, turning to stare at the half-elf shrewdly. "Not so, half elven. The balance is restored. The evil dragons will not be banished. They remain here, as do the good dragons. Once again the pendulum swings freely." "all the suffering, just for that?"
Laurana asked, coming to stand beside Tanis.
"Why shouldn't good win, drive the darkness away forever?
"Young lady?" Fizban scolded, shaking a bony finger at her. "
There was a time when good held sway. Do you know when that was? Right before the cataclysm!"
"Yes" he continued seeing their astonishment
"the king priest of Istar was a good man. Does that surprise you? It shouldn't, because both of you have seen what goodness like that can do. You've seen it in the elves, the ancient embodiment of good! It breeds intolerance, rigidity, a belief that because I am right, those who don't believe as I do are wrong."
Fizban is very clearly blaming the concept of good. He's saying "Good breeds intolerance, and the Elves and Kingpriest are 'good', but also bad for the world. 'Too much good' is just as harmful as too much evil is".
Dragonlance's take on alignment, like Mordenkainen's, is a trope called "Stupid Neutral" and a bit of the Golden Mean Fallacy. The belief that good is ultimately just as bad/harmful as evil. That mass murderers are just as important to the world as selfless heroes that save lives.
Relevant TV Tropes pages:
Some True Neutral people are devoted to the Balance Between Good and Evil - they fight only because the forces of evil grow too strong. Some just don't care very much about Good vs Evil (or Lawful vs Chaotic), only getting involved if their …
tvtropes.org
Good and Evil have rules they must follow. These rules are usually towards overall self-preservation; no one side is allowed to "win" too much. The Big Good and Big Bad restrict their fighting to a Cosmic Chess Game rather than going at it in …
tvtropes.org
Most people feel certain that there are two sides to every issue: their side, and the wrong side. Authors (and people in general) who subscribe to the Golden Mean Fallacy have another outlook. They believe that there are in fact three sides: the …
tvtropes.org
(Oh, and unsurprisingly, all of the attempts of trying to balance good and evil in Eberron always end with Evil murdering/banishing Good, taking power for themselves, and Good not having the resources and power to fight back against an overwhelming threat. Evil cannot be tolerated, because it's intolerant of good. Trying to tolerate evil just gives them the opportunity to take advantage of your acceptance. It's the Paradox of Tolerance.)