There's a couple agents complicit with the creation of the spirit bomb (that's what it's called now, we took a vote): Korra, for reopening the portals. Varrick and Zhu Li, for building the thing. All her minions for following along. The buck stops with Kuvira obviously, so it all falls on her. But it shows just how much goes in to a "bad" decision, and how blame usually is misapplied during the fallout.
From her position, as leader of the Earth Kingdom, she does have a "right" to unify her kingdom. She also stepped up, and through her indomitable will was chaos beaten back. All the world leaders recognize this. But her ascent was too swift and she's now too powerful, so Kuvira holds all the cards.
That's what Kuvira represents: the idea of an earthbender's indomitable will being taken to its extreme. She gets what she wants, and she wants power. To us that appears villainous, and the writers are laying it on thick with that re-education camp shit, but from her perspective she is asserting her will and doing "good" by restoring order. And she gets off on it, as it's plain to see.
It makes sense from her perspective, which is what I like in a villain: to be able to see things from their eyes. That old saying "if I don't build it, someone else will" applies here, I think. And if you have the means to monopolize power to further your goals, you carry the burden of using it.
I'm not disagreeing with you.