@Salfaro, everything you see in this chapter is happening in the Lunnet Imperial capital or whatever. It's not happening where the Princess, Nathalia, and Ar are in Rian although some troops were sent there thanks to MC letting the Jenneret noble guy go in Fendi. I don't think that last page in chapter 21 was not actually part of the story. Panels were pulled from within the chapter and put together for that last page. In other words, that last page isn't canon and if you scroll back up in chapter 21 you'll see where MC is having a conversation with Georgia and panels were pulled from it to create that last page to make it seem like Fendi was attacked.
@Siikalahna,
@dokidoki,
@doomer,
@SingLove, while I was annoyed with MC letting the Imperial noble go in starting town, I could see his reasoning by trying to let the Emperor talk to the betrayer, but of course PLOT happened and somehow with MC holding a giant sword to his throat, the betrayer managed to grab a nearby crossbow to try to shoot someone. In that situation, I give the MC a pass because, if memory recalls, he wasn't a soldier, police officer, etc. in his previous life in which he would've kicked away any weapons within reach of his captive. I also understand he needed more information about how many betrayers were within the supporter faction and how compromised their mission was. This was evident when he told Alice he felt they could no longer rely on anything from the support faction and had to make their own way after she had to kill the betrayer.
I also see this oversight (not kicking away nearby weapons) as potentially the over reliance on the fact he's strong and that nothing will happen to him so instead of thinking strategically, he thinks more like that. "Just muscle my way through this" in these types of situations. Not to say he never thinks strategically.
I don't see this as him trying to take the moral high ground on this one like he did with the noble. Supposedly when he talked to the Imperial Capital's sub-guild leader, or whatever it's called, Georgia, and learned that letting the noble go endangered the Princess, Ar, and Nathalia at Rian, he learned his lesson. He killed those showing an immediate threat and held the betrayer at sword tip for information. There's no indication there that MC would've actually let him live, nor Alice. I also see no problem in hauling the guy, if they could, to get more information out of them or taking a moment to do that.
@Tatsuya-Kai, I wouldn't call him a pacifist, I called him a quasi-pacifist. He doesn't want to hurt people, but does so when he's forced to do it. So when he's forced to make a decision like killing an enemy to prevent said enemy from talking and endangering allies and loved ones, he'll have a conundrum about it and likely fall back on his pacifistic tendencies or modern world, first world-like ideas where people would have a hard time outright killing someone defenseless in that situation. Especially when they don't have the means to imprison them while in flight.
@joel7686, I agree the MC is showing humanity in these situations. The only problem as has been said is that MC has been shown to take out people without much of a thought. As I said, he's sort of a quasi-pacifist, leaning on "not killing" when he feels it's convenient only to learn, like with the noble he let go, that it wasn't convenience, it was naivety.
@joel7686, in relation to you comment about him ending the war. MC's not uber OP at this moment, he's a mage that fights like a berserker and has the ability to level up. Also, there's no garuntee if he went on a rampage that the enemy would seek out and destroy the emperor. Also, he doesn't have all of the intel to know who everyone in Jenneret is in the Lunnet Imperial city. MC's actually doing the right thing with trying to get the Emperor out and into a safer place.
You also have to remember, the Hero had a difficult time fighting a high-level experienced warrior when we saw the fight from the hero's POV. MC hasn't faced someone like that yet. Bikini warrior girl at Fendi doesn't count. So even if it was within character for him to do that, I don't think it'd be feasible right now. So far he's dealt with a lot of fodder in conflict and not any serious threats. Of course PLOT could happen and the level of the threat may not matter as it sometimes doesn't for these OP MCs.