Why is that such an undesirable outcome? I already no longer exist in that world. Wouldn't it be better if I exited the stage before collecting so much collateral damage? And I think anyone would agree the world would be better if Shido had never risen to power.

Besides which, this is all still theoretical at this point. There are a number of conditions I'd need to secure before going through with it. Your ability to remember events from the original timeline would be one.