Sorry that should've read " Shinzon's motivations should've been the genocidal destruction of Romulus based on his background." I edited to reflect it. Well Shinzon says the echo triumphing over the voice was a goal for him. Legitimizing his existence by destroying Picard. Forging his own legacy and erasing everything Picard stood for. If Earth and the Federation were destroyed then everything Picard did, all the treaties, discoveries and battles he won become annulled since no one will remember him.