Heres a scenario;
You enter [insert generic town name here].
You see an elderly man being harassed by a young man with a knife.
You ask the young man with the knife to leave the old man alone.
The young man with the knife attacks you.
You kill him.
It turns out you just killed the mayor's son.
It also turns out that the old man was the leader of a local gang.
The mayor, realizing his only son is dead, kills himself in a fit of grief.
The town falls into ruin as the mayor's corrupted replacement embezzles all the town's funds.
Because that town was a key trading town, other nearby towns are rocked by a failing economy, as no one will buy their goods.
Poverty sweeps through the towns, and anarchy commences.
Once Civilized people turned to barbarians, murdering others in cold blood for food and supplies.
Eventually the towns run out of supplies.
The towns are abandoned, and their once well-to-do citizens wander the wastes to die.
Ok, so it probably wouldn't be THAT severe... But as you can see, the seemingly "good" deed of helping an elderly man resulted in the destruction of a large group of towns. I think it would be interesting for that kind of thing to be implemented more often. But not TOO often.