I guess part of it is maybe the fact that so much of s3e7 was a love story? Genuine, reciprocated love and devotion is… a weird thing we’re not used to seeing in villains since it’s all too common in works of fiction to go “This person is a bad person so they’re not allowed to have any wholesome or seemingly wholesome relationships.”
But I mean… Zarkon and Honerva so easily come to adore each other because, frankly, they’re both very ambitious people who never really had that many restraints about getting what they wanted. That strength of will, that hunger for power, and the fact that they had so much to offer each other- Zarkon’s resources and powerful political standing, Honerva’s bleeding-edge research and brilliant mind- drew them together.
They bonded the way people tend to bond- over finding common ground. And it just sorta comes back to, they enabled each other in incredibly dangerous ways.
Every time Alfor goes “hey, maybe this is bad, I don’t know if we should be pushing quite so far with this research, there are obvious consequences”- he talks to Honerva, but Zarkon intercedes- he either goes to stand behind his wife, or shouts Alfor down.
And part of it is how we hear people like Coran discussing it- how, I think everyone wants to kind of ameliorate their personal guilt that they didn’t see Zarkon and Honerva for bad apples before everything went too far. They want to separate the people they used to call friends, that Alfor presented his infant daughter to, that Allura may have known like a surrogate uncle for most of her life, from who they became, even when the seeds of that person were always there.
They were always ambitious. They were always cold. And in Zarkon’s case… he was never a person who could actually let go of people. We see it with Alfor, we see it with Honerva, we see it with the Black Lion.
Zarkon was not a white knight in shining armor who was consumed by darkness. He was a deeply flawed antihero and when met with someone who was his match in every way, the two of them spiraled downward, fast.
And I personally kinda resent the quintessence being framed as a scapegoat, especially when the writers have said that it more amplifies what’s already inside of you- and we see nothing corrupting about Voltron, that’s pure energy itself, and another entity born of the rift.
Especially because Honerva may have been overexposed, but Zarkon? Zarkon wasn’t exposed until his helmet broke in the rift. Every step he took down that path was his own. The only part you can possibly contest- his behavior after death- is consistent with who he was before.