In my eyes, the guards were basically babies who never had a chance of discovering what life truly had to offer, they were doomed since birth just like Meruem.
They were never "evil" (at least not Pitou and Youpi, in my eyes), their naturalistic senses simply told them that it was okay to put other creatures below you them create the world they wanted, and those senses were stronger than in the other ants. We live in a world created by humans who did the exact same thing, it's natural for that to be the first thing they try.
And yet, just like their ant side was strong, so was their human side, cause in their final hours they started to question everything. Pitou lived like, what, 2.5 months max? And on their first human interaction they started to feel empathy to the point of crying for Gon. That's crazy for someone who was literally wired since birth to do nothing but serve the king (and in the guards' case, love him as well).
You could argue that a main theme of this arc, and all of Gon's journey as a whole, is innocence. Gon was innocent about his own capacity to hurt people, especially with his powers and freedom as a hunter, and he realizes it while fighting a species that's even more new to Earth than him. This idea is shown in the Guard's names: They're a combination of names from egyptian gods (Shai, Menthu, and Nefertem) and names from a children's book (Pouf, Youpi, Pitou), because even though they're literal demigods on Earth, they don't really know anything.
When i see Pouf and Youpi crying over Meruem's body, it kinda breaks my heart cause that's literally their reason to live, in front of them, seemingly dead. What do you do with your life after that? Were they gonna kill themselves if Meruem was really dead? They hadn't even considered that possibility, that's how naive and idealistic they were. Meruem himself shows those childlike traits all the time, I could make a whole post about how he prefers play over duty and food, because his games with Komugi reveal that since the beginning he cared more about fun than anything else in his life, just like a toddler.
Pouf is the one that hurts me the most because he literally cannot live with his own emotions, he is so human that he basically becomes the real villain of the arc, he plots everything to make sure the love of his life gets to shine instead of being ruined by the humans, and the only thing he gets is a slow death while crawling towards his sire.
The tragedy of the Palace Invasion is that not a single hunter dies in vain, in fact, only Netero dies and he does it fulfilling his dream. Only the ants die, but Togashi made it clear that something important was lost that day.