The trouble with arbitrary societal consensus is that it’s arbitrary. And not necessarily any wiser than an individual’s personal desires.
These monks aren’t impulsively killing themselves, they seem to be towards the end of their lives anyway and are choosing how they want to go out. I don’t see what’s wrong with that. I might prefer to be in hospice hopped up on drugs when I pass, but I won’t claim to be morally superior for it.
It doesn't seem too wild to use irrational belief in something (faith) to make oneself happier through tough times.
It does seem wild to spend your final days in a pit alone until you starve/dehydrate to death painfully.