That's such a dishonest read of the book I don't actually know what to say. To me, joining Johnathan at the end is the conclusion of the entire book of love, loyalty and bravery. Nowhere does it say "meh, no biggie just kill yourself". If that's the message you took from it then I strongly encourage you to sit down one evening and read it again. The biggest "proof" of it not being treated lightly is obviously all the inhabitants of the valley of cherries enduring, surviving and fighting against oppression instead of as "just killing themselves" to go to the next level. Even at the end Johnathan makes it sound like it's a rumour and maybe there is something there, but no one knows for sure, same as naningalia was at the beginning - people hope there is a better afterlife, but that's all it is - hope.