The cringe never stops
The fuck could they possibly have done?
Killed some civilians? Started the war? Oh boohoo who the fuck cares
Samura talks about their sins, but he also says to Chihiro that "This is the problem", referring to Enten. It's not been explicitly spelled out, but logically it follows that Samura wants to chuck the blades into a deep pit... and it doesn't just follow, I think that's sort of the mainpoint. The talk about their crimes is just guilt over pulling the trigger, and also justifying why everyone in the know has to die. The trigger for what? Well, they probably gave their entire society some sort of magical radiation sickness.
The series keeps drawing parallels between the enchanted blades and nukes - they're weapons of mass destruction made out of some unique material that only exists in low quantities and only a select few know how to work with. Datenseki is clearly a parallel to Uranium. And... it isn't exactly uncommon for japanese works to feature metaphors about nukes.
Anyway, everyone has spirit energy, sorcerers can use spirit energy. The blades are
massive concentrations of spirit energy. Where does that come from? We've seen the Shinuchi suck the life out of others, and there is the detail of the life-long contracts preventing the bearers from using their original sorcerer - i.e their spirit energy - implying the blades suck it out of them. Using the blades heavily during the war probably fucked their society for good, and their continued existance/usage will make it worse. The generations following the war are all prolly gonna die early of magic cancer.
On a sidenote, Owl - a blind man that can see everything. Samura really is a walking contradiction, isn't he?