Shinzon's motives never made ANY sense. Why does he want to destroy Earth exactly? EVERYTHING that's revealed about him makes it much more likely that he'd want to destroy Romulus. The Romulans created him, the Romulans abandoned him and sent him to die a slow and painful death in the mines, the Romulans abuse, oppress, and mistreat his Reman "brothers." If the plot made ANY sense, then he should be attacking Romulus, not Earth. The only thing that Picard ever did to Shinzon was to exist, and without Picard, Shinzon wouldn't exist. Picard wasn't even aware of Shinzon's existence or who he was until Shinzon TOLD HIM. It's like the screenwriters didn't bother to apply ANY kind of logic to their characters or plot, how did the studio allow this script to be filmed, I'll never understand that. Still, Nemesis was NOWHERE near as infuriating as Insurrection, I HATE that movie.
Actually, his motives, as retarded as they are, aren't any more retarded than Nero's, yet Trek '09 is considered by some to be cinematic gold! In fact, Nero hanging out for like 25 years in space to blow up Vulcan and and try to do that to Earth, are even worse!