It is easy to kill people, unfortunately. Mathilde's done this innumerable times. Now, if you mean 'it should not be easy to kill people who are supposed to be on our side and havent really done anything wrong per se', I definitely agree.
But I would consider all the orcs and Skaven we've killed people, too. The necromancers and vampires as well, even though they were forsaken by the gods. People, all of them. I will refuse the argument that violence against them was 100% free of morality questions. 99%, perhaps, because they were causing active harm to people we care about and also they are in thrall to dark powers, but still: people.
Again, I would consider these extraordinary circumstances that are unlikely to be repeated. Boris basically told us he'd start a civil war for the sake of preparing Kislev for Chaos. If we'd stayed out of it, innocents would in fact have died and suffered and we could have felt quite guilty from that too. I would consider this minimizing suffering.
If Boris wasn't so explicit in all meetings we've had with him about repelling Chaos and strengthening Kislev, and we didn't know an Everchosen was coming, I really don't think we'd have gotten involved.
Like, let's say we'd gone to Bretonnia and one of the lords was saying that the current Royarch was bad, and he'd do a better job? I'd have voted 'no', even if it was an accurate assessment, because Bretonnia is not the first defense against Chaos - a Bretonnian civil war, while bad, would not so terrible that it could spell doom for the Empire, and it wouldn't be worthwhile getting our hands dirty for it.