Reminds me of a situation in Cyberpunk 2020 where I wanted to just knock someone out and rolled very well.
I killed him instead. Never really enjoyed playing with that game ref.
Is rolling high the same as rolling well?
I usually interpret a high roll as indicating some degree of skill. It always annoys me when my character's high bonus or die results make me more likely to screw up. E.g., I had a DM (back in the 3e days) who said when you roll a 1 on an attack you have to attack an ally -- using your full bonus. Shouldn't someone with a high attack bonus be LESS likely to hit an ally?
That said, I also think it's super-cheesy that a PC can deal huge amounts of damage with a giant nasty sword and then after-the-fact declare "oh I just knocked him out." So I think the sap is a good solution there, or some other house rule. But I'd try to discuss that with my players ahead of time.