The practice of defarbing your musket is just like anything else used by reenactors.
For example, you surely would not want to wear a pair of wear a pair of modern Nocona cowboy boots with your Confederate uniform and acutrements after spending $600 on the uniform and equipment to be accurate. Even if most spectators at the reenacting events would never notice the difference.
If you are just a shooter, there is no reason why you should to defarb a musket.
Using an old original musket for reenacting is not an option for the same reason reenactors don't use original uniforms and acutrements. That is why they offer to defarb new muskets and sell new uniforms and acutrements.