You mention that there are "philosophical and practical grounds" to oppose this kind of "restauration", yet you say that "it's a shame" we cannot do it, suggesting we should indeed prefer erasing centuries of Italian history to please tourists and attract more funds.
It is remarkably funny how the "return to order", "purity", "glory of the roman empire" was exactly the same rhetoric and aesthetic of the Italian Fascist party. I guess this could be counted among the massive missteps you mentioned?
I think you would have a much better experience if you just enjoy the stratification of history and art that Rome, Italy and the Pantheon represent instead of projecting a subjective idea of how things should be.
And yes, it's a tacky mess at times, but is not up to you, tourists, a party or even a government to decide on a scale of dignity of historic periods.
edit: added Raphael's wikpedia page reference