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.
Being bad or evil is literally bad for your health.
The better you act, the better your health - great teeth, good muscle, low fat, high fitness, good looks, and longevity (to a point), no addiction or mental health issues, selfless with no crazy ego. Ie Mother Teresa looks like a supermodel!
Health can fluctuate based on behavior but it always drops 3x faster than it improves. So if you fuck around on your wife, your teeth go bad, or you start balding etc. cheat on your taxes, or lie maliciously (excl. good lies like Santa) you start to get fat n ugly.
If you’re a miserable prick who fires staff, scams people, bribes, hires children for sweatshops or harms people just to increase profit or boost share price you get cancer. But if you help those people then you may be cured provided you handle it really well and undo all the damage.
You attack someone, pedal harmful drugs or hoard unnecessary wealth, you go blind/deaf until you earn it back, more than once and it becomes permanent, each time after that you lose a limb for good.
You intentionally harm or kill someone via murder, drink driving, rape etc then it’s game over via a slow, long, painful debilitating disease that’s contagious to anyone you like or care about, ensuring you die alone.
To help identify the good/bad, your gut instincts are 10,000x more powerful and obvious to warn you of the dangers or benefits of each choice.
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.
A disease that kills everyone a bad person knows, even if they don’t do anything wrong, is a Bible level of justice.