I don't find what's so cute about it. It's the opposite of "cute".

[He tilts his head back with a loud laugh at that, like Dazai told him a particularly good joke.]

"Is it more idiotic than wanting to live"...haha, what, trying to be all philosophical on me, huh? What a joke! If you've tried out so many methods, why haven't you succeeded yet? Are you just being extra picky?