Look characters in a game change that is how things happen in a video game. Cain changed from being apathetic to a scholarly loremaster that helped us in D1 and D2. Tyrael changed from being the Angel of Justice to just a man. Even though going back into heaven it doesn’t say if he will be seen as the aspect of wisdom or not. Then there is Malthael changed from being the angel of wisdom to the angel of death a villain of D3.
So what Rathma is doing could be seen as what he thinks is the best thing to do. Characters in a game can be misguided or misled by themselves. Rathma isn’t some perfect god that will never make any mistakes.
We have to look at it as the way that the game shows us. If what he is doing is wrong then we must stop it. Even if he mistakenly believes it is the best thing to do.
Having characters in a video game that don’t change with the course of time is not realistic in the game let alone the real world.