Questioning is one thing - dismissing is another. I do not like being strawmanned.
The one moderate Garlean we've met is Regula, who was still a racist. Forming an alliance of necessity... doesn't change that. Don't forget that he had personally tried to kill us three times by then. Yes, we killed some of his men - in self-defense, and without an option to show mercy it's not really fair to hold that against us. I'm not trying to downplay Regula's virtue - he was honorable, merciful (well, to little kids), and had his nation's best interests at heart, as shown by how he decided for himself that the Allagans' methods were too flawed to use. I'm just not letting his vice be ignored.
Gaius is not dissimilar. He had standards - he didn't want to glass Eorzea or use chemical weapons to kill its population, and had a very meritocratic philosophy - but don't forget he still tried to take away Eorzean sovereignty, twice, for no greater reason than because he considered its leadership inept and believed he could do so.
Morality is a very complex issue, and I don't and won't deny Garlemald is more complex than "muahahaha evil Empire come to take your stuff and kill your people 'cuz we can." Regardless of that, it has not attempted any diplomacy except at the point of a sword and has not been shown to do anything but tyrannize its non-Garlean subjects, with the minor exceptions of Rhitahtyn and Fordola (and maybe Grynewaht before we repeatedly defeat him). As somebody who leans very heavily toward Chaotic Good on a standard D&D morality chart when unbound by the laws of the real world... I can't really abide, because freedom is very important to me. (Seriously, I don't enjoy games like Grand Theft Auto because I don't see the point of doing all the... well, unnecessarily violent things you can do, despite having the freedom to do so.)
Having reasoning behind what you do doesn't make it right. As I said, I'll use Spider-man: Homecoming's Vulture (easily the best part of the film; the rest is pretty standard Marvel fare these days) to illustrate my point. Hide-boxed for spoilers.
In the film, Adrian Toomes (the Vulture) starts out as a pretty average man - demolition cleanup, specifically cleaning up after the Avengers' battle with Loki and the Chitauri in the first Avengers film. After purchasing a lot of equipment using debt to clean up the mess, a government agency comes in and relieves him of the work. After returning to his office, he finds one of his trucks still had a piece of Chitauri technology on it - and one of Spider-man's lesser foes, the Tinkerer, is part of his crew. So they set up a black-market version of what Stark Industries used to be - using scavenged tech to make weapons and selling them, making "Vulture" a very fitting moniker.
This continues for eight years until Spider-man brings him down.
Now, what makes him sympathetic is that he is doing this for his family. He claims himself a family man and, since Peter Parker's love interest is his daughter, we do see him in a civilian context and it is absolutely true. He is also very reasonable with his subordinates, only killing one by complete accident and otherwise listening to their advice while reprimanding them for being stupid. He was also flying under the radar and keeping his operation small enough to avoid government detection - it wasn't until the Shocker idiotically decided to demo some of the weapons in the suburbs that Spidey got onto his case, leading to his ultimate downfall.
The question is: at what point does it change from necessity to simple greed? Remember, eight years - that is more than enough time to clear his debts and find honest work. By the time of the film he has quite an opulent home for suburban New York.
The same question I would levy on Garlemald: at what point does it change from necessity to simple greed? They have long since reclaimed their ancestral homelands and gotten revenge on those who wronged them (though I don't encourage revenge - see 3.0) - why it it necessary to invade other nations? Is two and a half continents not enough? Do they not realize primals are summoned in response to their invasions, not the other way around? Is diplomacy not worth the effort? Do the lives of others not matter?
Also I'm just gonna take a moment to fanboy over the Vulture's design in the film. He's creepy and scary for a villain who normally poses very little threat. His wingsuit has glowing green eyes and freaking talons!
... having a reason doesn't make it right. Even Zenos had a reason - albeit a more self-serving one than any other Garlean thus encountered. (He still earns a twinge of sympathy though, especially from people who did not have many friends growing up. Varis is now getting close to being in the running for "Best Dad on Hydaelyn.") To fight - to kill - in self-defense, to preserve sovereignty, and/or to liberate from oppression is not wrong, I don't think.