Ironically the mediation tools you likely use were developed originally by people who did do the insane and dedicated far too much time to meditation.

It's true that the monks you refer to are extreme in their devotion. Their conviction for this comes from a religious absolutism so it's not hard to see that when mediation practices are devolved from that context they become much more moderate.

To be specific, every one of that kind of monk believes in reincarnation so it's not so much a wasted life as a preparation for the next, and the eventual release from the cycle of suffering which in fact is life.

Certainly any belief system which fundamentally rejects life and takes metaphors of death and rebirth literally has crossed the threshold into the insane, but I would be careful about throwing that term around.