From that EG thread:>I'm sure that Beautiful World and Sakura Nagashi aren't sung from the perspective of Kaworu for two main reasons.
1) It's a woman's voice, and I don't think they do male narration by female singers. In "Everything You've Ever Dreamed", for example, the final song has an entirely third person perspective of Shinji being interrogated by the female narrator (ie. "What was it she did to break your heart?") The original Japanese lyrics did have first person elements, which were probably meant to be sung by a male. Komm, süsser Tod is surely from Asuka's perspective. Reading those original Japanese lyrics confirms it beyond anything. "I'm afraid of being disliked by everyone." - "I mustn't let myself like anyone." - "If I entrust my heart to another, I'll be devastated in the end" - those are all pure Asuka.>2) The songs contain many elements of strong human empathy that are not compatible with what we see from Kaworu.
Kaworu is interested in humans, but he isn't one. He's as far estranged from humanity as you can get in the NGE universe. Not just a god, like Rei, but the god of the angels.