Okay. So RTN has a really weird setting that I don't quite have time to explain how/why I think it works, but the short of it is 1.RTN!World is a REAL alternate universe, and 2. much in that world is preselected to fit Naruto and Sakura's vision of a perfect world.
This makes Menma a WEIRD character, but I do have an explanation for that too; The movie takes place right around the time of the waterfall of truth where naruto, famously, does not actaully address his own deep set repressed frustration with the village. Why does Menma randomly go missing nin right before Naruto and Sakura show up, despite living a well adjusted life? Because in the same way that Sakura secretly would prefer her parents dead and famous, deep down Naruto wants to see a world where people care about him as much as he cares about Sasuke. A world where if he went missing nin, even if he was as deplorable as the Akatsuki, he'd have friends and parents willing to give him the benefit of the doubt and do anything to bring him back. Naruto's biggest fear is becoming a monster, because he's already spent his entire life trying to redeem himself for being born, and if people can barely forgive him for being born then they'd never forgive him for actually living up to the expectation. So, of course, Tobi would send them to RTN world just in time for Naruto to see a world where Menma is loved. unconditionally. People love him. People can love him.
