The Andalites are like the biggest Karma Houdinis of this series. The entire series, of course, it about dealing with Yeerk imperialism, but the Andalites are largely allowed to get away with the colonization of their own. The Yeerks, were, after all, the by-product of an attempted Andalite “uplift” of another species.
Before the Andalites landed on the Yeerk home world, the Yeerks seemed to have been a pretty content species. They are implied to have been the only sentient species on their planet, and co-evolved with the Gedds to form a symbiotic relationship; most Yeerks never left the pool and so while they are very intelligent, they don’t have much ambition and could live their lives without ever wanting more.
Then the Andalites show up. Seerow sees potential in them, and gives them access to technology and knowledge of the stars. Suddenly, the Yeerks want more. But the Andalites will not give them more. They have shown them a world outside their own, and then told them to stay in their pools. And before the Andalites arrived, no Yeerk ever hated their own body. But suddenly this imperialistic species has arrived on their own planet, calling them “parasites” and “filthy slugs” and suddenly having a host is the most desired trait.
We don’t know what circumstances led to Akdor 1154 leading the rebellion to steal Andalite technology and take off, but we have reason to suspect that it wasn’t as clear-cut a “betrayal” as the Andalites made it out to be.
And the lesson the Andalites took from this? Ax says in the #8: The Alien, “Once we were kind when we should not have been kind.” Meaning, they have pretty much learned nothing, except leading to their being even more xenophobic to species not as “advanced” as their own.
Take a look at how they view the Taxxon species. The Taxxons got the short end of the evolutionary straw: at some point in their history, the Taxxons must have faced a time of great starvation, because they have a deeply-ingrained fear of not having enough to eat, so they have insatiable hunger. And that leads to them being cannibals. They ally with the Yeerks on the small chance that the Yeerks might be able to control the hunger, which is very tragic.
But to the Andalites? Elfangor talks about the Taxxons’ “evil instincts,” their “evil bloodlust,” and calls them a “seriously ugly species.” He’s met Taxxons who resisted the Yeerk Empire, Taxxons who wanted to drive the Yeerks out of the Living Hive. And yet when he gives the morphing powers to the Animorphs, while he tells them the Hork-Bajir are a good people, he says “The Taxxons are evil.” And, by far, the Taxxon-Controllers have the biggest body count, by virtue of both the Animorphs showing no resistance to wiping them out, and their skin having the density of rice paper so that even a paperclip could take them down if you were close enough.
And of all the alien species encountered, the Andalites have the most genocides or attempted genocides under their belt:
“Anyway, The Five discovered the Venber and began to trap and export them.”
“Say what?”
“They basically harvested the Venber. It seems that a Venber melts, burns, in any case becomes liquid at temperatures above freezing. And the resulting liquid has many uses. Particularly in the creation of superconductors for the primitive computers of that era.”
"But… But these are sentient creatures, aren’t they?” Cassie asked.
“Yes,” Ax said simply. “They were. The Five extinguished them. They annihilated a sentient
species to speed their computers. The Venber disappeared.”
“That’s sickening,” Cassie said. “That’s just evil.”
“Yes,” Ax agreed. “But if it is any comfort, The Five are no longer in existence, either. Soon after we encountered them for the first time they… well, no one knows for certain what happened to The Five. But Andalites in that era are not the Andalites of today.”
(Animorphs #25: The Extreme)
Now we know nothing about The Five. It’s entirely possible that the whole species was just as bad as those that wiped out the Venber. But then the Andalites have a strong history of casting their enemies in moral absolutist terms (calling all of the Yeerk and Taxxons “evil”). And then, of course, we know that Ax is either lying or mistaken when he says that the Andalites then are not the Andalites of the present day:
This virus was an admission of failure. The Andalites couldn’t save the Hork-Bajir. So rather than let them fall into Yeerk hands, they would annihilate them.
❮l didn’t know,❯ Aldrea said. ❮l didn’t know. This is wrong. This is wrong. They can’t do this.❯
“It makes perfect sense,” I said. “To the brilliant, ruthless mind of an Andalite, it makes perfect sense. They would rather destroy us than have us become tools of the Yeerks.”
❮No!❯ Aldrea cried with more force than I’d ever heard from her. ❮No! That is not how we are. Alloran has lost his mind. The Electorate will never support this. Never!❯
“Maybe not,” I said. “But the Andalite Electorate is not here. Alloran is.”
❮We are not going to let this happen,❯ Aldrea said. ❮We are Andalites. We do not destroy sentient species.❯
(The Hork-Bajir Chronicles)
Despite the Hork-Bajir having served as their allies during the war, the Andalites consider them acceptable collateral damage. And we know Aldrea is wrong: Andalites have destroyed sentient species in the past. We may consider her, like Ax, to be the product of a world that have hidden its less-than-stellar moments from their populace. After all, according to The Andalite Chronicles, it’s revealed that while Alloran was made the scape-goat and ostracized (the Andalite government seems fond of making individuals scapegoats, as they did with Ax for Elfangor’s breaking of Seerow’s Kindness), the majority of Andalites were told that the attempted genocide of the Hork-Bajir through biological warfare was a lie:
A quantum virus is a sort of disease of space-time. You see, it slowly breaks down the force that holds subatomic particles together. It slowly disintegrates whatever it affects. Living creatures affected with a quantum virus find their very molecules breaking down. It can take days, weeks of agony.
That was Alloran’s secret. That was his disgrace. The Yeerks had accused us of using a quantum virus against them. We had denied it. Every Andalite believed it was just another filthy Yeerk lie.
The Andalite military lets the Yeerks take the fall for the genocide of the Hork-Bajir and keeps their citizens in the dark about their actions. It’s to the Andalite home world’s benefit to let their citizens and soldiers believe that the Yeerks are lying about their own actions because it would keep them motivated and keep them from questioning their orders.
And lest we think that Alloran was just the only Andalite to find this mode of warfare acceptable:
“We have to stop Arbat and we need fire-power,” I said.
“Why? To save these filthy Yeerks? Look what they do. Look at what they are! They are going to do that to us, Aximili! They will drag us down that pier, they will force us … NO! Kill them all!”
"Estrid, you said the virus may mutate. You said it might affect humans as well.”
"Might. Maybe. But maybe I fixed it. Maybe my last adjustments eliminated the random flux. I do not care! They are not our people. I am not going to let the filthy slugs do that to me!”
(Animorphs #38: The Arrival)
Estrid and Arbat were sent on a covert mission from the Andalite high council to wipe out the Yeerks with a virus – and if humans were caught in the cross-fire, well sucks to be them. And apparently that policy was so nice, they attempted it twice:
❮The high command has met and made their decision. If the Yeerks are indeed concentrating on the planet Earth, we must allow their plan to continue. Once the bulk of the Yeerk race has been transported, the planet can be quarantined.❯
Quarantined.
A polite word for consigning the human race to a life of slavery under the Yeerks.
—
❮Once the planet is quarantined,❯ War Prince Jaham continued, ❮we will be in a position to negotiate. We will mediate a peaceful symbiosis between humans and Yeerks.❯
I wondered if this was an accurate description of the Andalite high command’s intention.
—
Quarantine. Quarantine. Quarantine.
It was just a way of saying what could not be said over any channel of communication, no matter how secure. Because it was something that could not even be said in the chambers of the high command.
The stated goal would be to quarantine. The orders would say to quarantine.
But what everyone would understand is that a quarantine would be impossible to sustain.
To enforce a quarantine, the Andalite fleet would be forced to engage.
And once they engaged, they would annihilate the planet and every living thing on it. Yeerk and human.
Quarantine was the first step toward genocide.
(Animorphs #52: The Sacrifice)
But at the end of the series? We’re BFFs with the Andalites, despite that even tho the Yeerks treated us like cattle, they never tried to wipe us out. No Taxxon ever committed genocide, but because they’re ugly and have a evolutionary trait that’s undesirable, they’re made into nothlits dumped and in the rainforest to be forgotten. Humanities enemies deserved punishment, but the Andalites, being our allies, pretty much get off scott free.