As a subtlety may I suggest a substitution of adjective? I believe the term I used with regards to units was brittle, not stale (though I may well have mis-stated myself). Stale implies that the unit has been left on the shelf too long. John Cook has also written on this matter of units becoming brittle on at least one of the fora. You may want to drop him a line. The analogy would be to a piece of steel left in the fire too long, then shattering under the blacksmith's hammer; or, leather work used too long and hard until it starts to rot and shred.
By comparison, individuals suffered from some form of PTSD are often described as brittle as well. Brittle carries connotations of being overhardened, liable to disintegrate unexpectedly, shattering or crumbling on disintegration.
One example that comes to mind is the panic of Lasalle's brigade at Golymin. That certainly looks like an over-used formation that just fell apart.
As for the forlorn hopes, there would be all kinds of motivations from suicidal, to maniacal, to a belief in being the best soldier for the job, to bravado, to loosing a bet, to volunteering out of shame for over some other incident. Each man would have his own reasons. I'm sure that some volunteered because the CO "suggested" that outstanding disciplinary actions would proceed otherwise.