If all of the Royal Guard act robotic to a fault, then how come this guy that was a Royal Guard ended up going on a murder rampage because he was racist against Adventurers? I know he got possessed by the sword Byakumaru, but his article said he only took the sword in the first place because he already wanted to kill the adventurers. It just seems inconsistent that a Royal Guard would have feelings.
They've always had feelings, just like any Lander after the Catastrophe.
The robotic part is their detection system, which only revolves around the basis of Combat actions within the city. So they only respond to actual weapon clashing, combat spells cast, and/or HP damage sustained. No other Guard reacted to Kyouko's clash against Nelles because he had the Royal Guard armor on, so their detection system reported her incident basically as "A Guard is already on the case" and not "Someone went rogue and is attacking Adventurers."
Right on the Royal Guard page it states that "the Royal Guards seem to ignore whatever words are spoken to them. " and "Their overall behavior, except for one, [Enbart Nelles], seems to be robotic, and none of the Royal Guards have [any] perception of morality, so they are incapable of discerning right from wrong." and that section mentions a story where an Adventurer and Lander were almost getting raped but the Royal Guards didn't understand or react to it, except when the victims tried to fight back, which then made the Guards target them instead of the assaulters.
So why is Enbart so different that he can break all those rules?
Yeah, because they're doing a job. It's like having a control room and when combat occurs, it appears on the map and a Guard is dispatched there. Rape/sexual assault does not deal any HP damage or count as a combat action, because it wasn't even possible before the Catastrophe and thus doesn't show up on the Royal Guards' detection system. Isami drew her sword and cut the person, making them bleed/take HP loss, which counts as a combat action. Guard is summoned.
And obviously they're going to act differently once they're outside of their suits. Enbart's entire motivation is that he hates being treated like a mindless object and doesn't think that he (or the Royal Guard) are getting the respect they deserve. To quote from volume 6: "The proud guardians who protected Akiba. However, they weren't honored. They were scorned as pseudohuman automatons. Although their abilities surpassed even the Adventurers, their status was, at best, security devices, and they were essentially treated as nothing more than accessories for the town. They were a tribe of dogs. Truly a clan of slave-warriors, offered up by sacrifices, just as the characters in the name Kunie implied."
When the Royal Gurd actually did show up to the scene of the crime though, it still did not care even when a Lander tried to explain the situation to it. A Lander understood that a sexual assault was going on, but the Royal Guard didn't and didn't react even though it was right there having the situation explained to it. That makes me doubt their humanity, and if they can't react like they have any while in their suits, then they kind of deserve the way they are seen. I don't remember ever seeing any other Royal Guard Landers outside of their suits though.
Royal Guard Landers outside their suits don't announce they're off-duty Royal Guards. In the anime, Enbart Nelles is seen walking around before he buys the cursed sword and nobody knows that he's one of the Guard until he starts going on a rampage and people start connecting the dots.
Long story short, to go back to your original question, your assumption is that Royal Guards are another separate type of Lander. They're not, they're the same as Rayneshia or Kinjo or Sara. It's just that they act differently when they're on duty, and it just so happens that Enbart Nelles was pissed about his situation where others weren't.
I think the original question was asking why there seems to be inconsistencies with the portrayal of Royal Guards and their feelings. More often than not, Royal Guards are shown to make emotionless robot-like decisions, acting more like an NPC than how People of the Land act after the Catastrophe. A good example is in the West Wind Brigade spin-off manga where the Royal Guard only obeyed its would-be programming. In other settings People of the Land act more human-like and make their own judgement on what they should do for their job or their lives, like Enbart Nelles who decided to leave the Kunie Clan and go on a killing rampage. Even if the detection system only found violent acts that are actual combat actions, it would make more sense for the responding Royal Guard to understand that the real situation was self-defense and the sexual assault should be stopped. Instead responding Royal Guards only act on the detection systems rules and have no personality of their own.
In the end I have no answer, it doesn't make sense to me either.
Because they're doing a job, and their job states that they are required to punish those who commit violent acts inside noncombat zones. It's like how people who kill in self-defense can still be charged for murder (or manslaughter?) even if it was done in self-defense. There's no inconsistency at all, since we don't actually meet a Royal Guard in the novels until volume 6.
Royal Guard rules are also bizarre on their own, because on one hand the novels stated they lock people in prison if someone misbehaves in a noncombat zone (which seems to be the only situation in which they appear), but then it's also stated that they just kill players who are involved in combat. I figured that Royal Guards lock people in prison unless the person fights back, after which they would be killed (would be consistent with the LH official manga), and the WWB manga did its own thing like usual. But then volume 2 stated that anyone who breaks the rule would meet death, so :/
Seems to me more like a plot hole for story convenience.
If the guards weren't robots and actual people, it shouldn't be too difficult to convince them to help take out a rogue member. It should be a major embarrassment to them and a gross neglect of duty to let a rogue member go around doing the sort of things they should be preventing.
Once they've agreed to cooperate it shouldn't be too hard. The guards seem to be able to teleport in at the first sign of trouble, so if attacking a guard doesn't trigger their monitoring system the patrol members could just attack each other in a certain way to get a bunch of guards to teleport in to take out Enbart.
If multiple guards can't be in the same area at the same time that would mean the guards can't be very effective in stopping many high level adventurers insisting on doing PKs, since it takes them some time to take down higher level adventurers.