Correct, but that ideology is expressed through curation. The challenger record displayed as "Humanity's ambitious first attempt to contact their neighbours more thsn two centuries before developing FTL, kindly on loan from our friends at Terra" is an ideologically different exhibit to one labelled "Horrible Xeno Pornography shot at our planet to corrupt our youth". If we're going for mechanics as realism the most sensible mechanical result would be that after liberating them you quickly rearrange their collection to display everything that bumps ethics draw toward their new government ethics.
The only mechanical reason to blow it up on conquering is so your empire doesn't end up with two GAs but liberation wars don't give you the system anyway.