Because you need to know how the world works before you can predict the impact of an action. That's not hard to understand, I'ld think.
For example...
Take plumbing. The word itself betrays its roots: the latin plumbum, which means lead.
In ancient Rome, lead was the material of choice for plumbing. Little did they know that lead is highly toxic for humans and that using it for water transporation is very very bad idea health-wise.
Today, through science, we know that it is a health hazard.
If TODAY a plumber would use lead pipes, it would be extremely immoral, because common knowledge dictates that this water will end up poisoning people.
So, that's how. Through science, we learn about reality. Through science, we learned that lead is very toxic. So, we stop using it for plumbing.
But outdated. Why would you base anything on outdated scientific models, which have been replaced with newer and better ones?