Why should this church be protected when it is built upon an aztec temple?

This is regarding the metropolitan church in Mexico city where the time capsule was recently found. I have a hard time trying to understand why there is such a push to restore the church when they should demolish it in order to restore the temple which it is built upon. The aztec civilization and some of the other hundreds of civilizations that existed here before the exploitation initiated by Columbus were some of the most extraordinary cultures to ever exist.