I guess mostly I'm not buying that such a setup could last for more than five minutes. Like, if it crumbles once the heroine (presumably) starts pushing against it, why didn't it crumble long before then? Is it a brand new system? What's going into keeping it in place? Why is humanity standing for it, basically. What kind of terrible thing happened as a result of NOT having these categories that keep people so afraid that they accept them? Or, conversely, what kind of benefit are they getting from it that's impossible to get in a setup that actually makes sense?

I guess I just want to know if the worldbuilding is any good.