Alderaan was a planet of dangerous insurrectionists who had infiltrated the upper echelons of Imperial power, but the planet itself represented only about 1/1,000,000 of the Empire's population. To put that in perspective, scaling the Empire down to the United States, Alderaan would be about 300 people. Killing 300 of our own citizens to put down a few insurrectionists would be highly unpopular, but the scale is similar to the Waco siege (80 dead). It might bring down a few officials, but it would not make the United States "evil." I suspect the Imperial populace viewed Alderaan much the way we viewed Waco--a regrettable overexercise of Federal power, but they were a bunch of trouble-making crazies anyway, and probably deserved it.

As for Padme, she is written exactly the way she is supposed to be: a super-elite and elitist bimbo, who covers her love of power and all its trappings by giving lip to "liberty." She reigned over a deeply segregated society, a human elite literally towering over an amphibian race confined to underwater ghettoes. This is the world that propelled Palpatine into the Senate; is it any surprise the Empire was apparently segregated and human-heavy at the top? (Nor did Padme's daughter escape this poisonous atmosphere when she was adopted into the blood royal of Alderaan. Leia's disgust when confronted by low caste aliens is so overpowering she cannot help but use a slur against the Wookiee who rescued her from execution on the Death Star!)