great question. = 'can they suffer'. I believe this to be a great question for today's world. But - in the same thread we are speaking of horcruxes - so we have to place our reasoning in Harry Potter world and wizarding belief - yes?


a horcrux is made upon the killing of a wizards life - cause the murderer's soul to be split.
In HP - when a wizard maliciously kills, their soul splits... and they can put this fragment into an object to preserve a part of them.

when the Order kill Death eaters - I do not think their souls split or fracture as a result. I don't think Molly Weasley has a fractured soul. I think she killed Bellatrix out of love for her kids. It was love, adrenalin and unbearable pain that gave her the rage to 'really mean' to kill Bellatrix.
(do we know who it was done? did Molly use Avada Kedabra, or could Molly have used another spell, perhaps caused stone to fall upon Bellatrix, cause Bellatrix to impale herself on something.... could Molly have used smarter magic to do the job?)

Something new to think about. It must be a 'murder' - 'malicious'.
If you kill for self defence & the greater good - I think it is ok. somehow - magic has 'morals' perhaps. It knows the difference between a 'good kill' and a 'bad kill'.

What do you think?