Contemporary historic preservation sees itself as the guardian of historical substance. The content of a monument is bound to the preservation of the inherited material.

Georg Dehio’s principle of "conserving, not restoring" is often invoked as a synonym for this self-conception. Old and new need to be clearly separated.

It is a counter-movement to the 18th century historicism which ”destroyed” a lot of old monuments beyond repair.

Personally, I think we went too far on the conservation angle (at least in Germany, not sure about other countries), and should restore a bit more again with the knowledge we have. But much more intelligent people have debated that for centuries, so I guess their answer would be the same like https://askastaffengineer.com/.

I'm in the conserving camp. It's more truthful than the narrativization that accompanies attempts to restore. We should remember that we all had a reptilian vision of dinosaurs for decades (centuries?) before the latest feathered view. We would have been better with neither. Just display the bones: what we have. Everything else burdens the public with guesses.