Let's be more specific. Do not use propane indoors.
It produces CO, it can tip and cause fires, and unburned propane is heavier than air, which can pool in basements and go boom. (Natural gas is lighter than air...)
Lots of homes are using propane inside. Stove, dryer, waterheater, gas logs in the fireplace, etc.
If you are safe in your application you will be fine. Propane produces no more CO than Natural gas.