Actually, I agree it's time to get the discussion back more specifically to the Russian palaces. However, I thought the digression was useful because if one approaches the question of why did the Germans destroy the Russian palaces from the perspective of a belief that only the Germans have ever done such a thing or that the German destructive acts were somehow more heinous than other similar acts by other belligerents, one will arrive at an answer that is wrong, at least in part.
Different conquerors have different agendas. Cyrus the Great and Alexander the Great wanted to control as much of the earth's surface and peoples as possible, but they did not strive to elevate any one culture or religion over another into the bargain. Napoleon wanted to impose French power on all of Europe, but it was his personal vision of French power, as his Continental System was as foreign to French tradition as it was to other European traditions. The colonial powers wanted to turn the less-developed world into their cash cows with as little bother with other things as possible.
But Hitler was in that class of conquerors that arrive on the border with an ideological brew on the boil. Eastern Europe was not to be conquered for the service of Germany or even for its populations to be integrated into German culture and the German economy. It was conquered to be cleared out to make room for the expansion of the pure Aryan race and its equally-fictitious and quickly-fabricated culture. While some populations -- the Jews being only the most infamous example -- were literally to be eradicated, other populations were too vast and entrenched, so their destructions were to be accomplished more through symbolic means than physical. And with that came the deliberate destruction of their cultural heritages.
I earlier mentioned Hitler's plans to turn Berlin into Germania. To understand what Hitler was really about, one has to understand that it was not German culture he was trying to impose, with its odd mix of militarism and liberalism, straight-laced propriety and cabaret excesses, Lutheranism and Catholicism. It was a bizarre Nazi fantasy of Aryan culture that cherry-picked elements of German culture, poured in a few Nordic fairy tales, stirred in a few noisy Wagnerian operas, and grossly distorted some borrowings from German philosophers whose undistorted philosophies were frightening enough.
To understand what Hitler did to Russian palaces, once must remember that Hitler put a gun to his head, finally convinced that even Germans had proved themselves undeserving of the glories he strove to bestow on them and that the Fatherland itself had earned its own consignment to flames.
To me, this was the essence of what drove the German destruction in the St. Petersburg area. But, even at this extreme, Hitler was not unique. Eradication, not integration, of native populations and culture was the first order of business of the western European conquerors in the first century of their expansion into the New World. And, in only a slightly less brutal degree, it is what Russia itself had been doing for centuries with the Jewish populations it absorbed as it expanded its borders beyond old Muscovy. The Pales of Settlement, pogroms, the May Laws . . . the impetus to cultural eradication of rival tribes (to use an anthropological term) is a universal element of human nature that is kept in check only by sophisticated social organization and that pops right back to the surface when things such as war stress that organization.
At least we can be grateful that the Russians have proved adept at rebuilding their magnificent palaces.