The rule could be anything, as funny or as serious as you want. The universe will progress in a similar way that it has up until this point, unless your changed rule prevented it from doing so.
Some examples might be:
- The invention of currency is not allowed.
- Iron is slightly less stable.
- The Ancient Greeks are able to cultivate Silphium, which does not go extinct now.
How is “being bad” decided?
If it’s decided internally (“bad” is what you believe is bad), then all the objectivists get a free pass for being assholes. Hitler is a supermodel, etc.
If it’s decided externally (there’s an universal definition of “bad”), how far into the future does it propagate? If I rescue from drowning someone who will genocide all the Dutch in the future, when do I go bald?
That said, beauty pageants would be much funnier, with trolley problems instead of talent competitions.
This is why this one wouldn’t work in any meaningful way. Good and bad is a human creation subject to the individuals perception.
I think they are saying that in their revised universe there would be an absolute humanity spanning moral code.
And the things that that moral code decide are bad are bad always for everyone regardless.