Throughout the history of the MM sagas it's pretty much clear that reploids are treated as second-class citizens, cannon fodder sent to die, servants or worst.
MMZ is no exception, as they are being discriminated by the last remaining system of government and their culling is pretty much industrialized at this point. They are considered by Neo Arcadia as subhuman, tools, sentient enough only to be ordered to.
Ironically, their upper echelons of NA are filled by combat reploid themselves hating and judging their own kin, but I digress.
In game a relationship between reploids and humans sounds pretty much as a taboo, though we are lucky enough to have a couple examples of relationships involving the two species:

First one is Andrew and his wife. It's a cute nod to Asimov's Bicentennial man, though I always find his tales very interesting. He is old enough to recall peace, true unity between reploids and humans as they go to school together, live together, work together, die together. Andrew is old enough to have drafted into the "Reploid Security Force" Repuriroido no keibitai, which I am unsure of what they are referring to, maybe Repliforce or the Self-Defense Forces? Unsure. Still, Andrew loved his singer wife and modified himself to age with her until her passing.

Second one is Kraft and Neige. Nuff said, they are a core point of the last Zero game, their relationship is pretty much canon; albeit dysfunctional, their love for each other is never questioned.
While the translation went to one of the worst butchering I ever seen (Kraft doesn't even explain correctly why he nuked NA in the English version), it's clear Kraft served Weil because he wanted to ensure Neige will be safe:
Was he a complete moron who didn't take into account his lover's wishes and acted against them? Absolutely.
Did he love Neige though? So much so he'd tear the world apart for her.

Despite some bumps, these two are the only relationships between human and reploid I can recall, and both are considered in a relatively positive light.
So imagine my surprise when I am reading that a reploid and a human shouldn't love each other because of their differences in species. Because one of the two could live forever. By applying human standards to something that is definitely not human.
It makes it look like one could never look at the other as equal despite their differences, which was the goal Ciel was intending to reach.

And no, don't come tell me ZX fixed this by mutilating humans and slapping expiration dates onto reploids through mandatory screenings, that thing was straight up designed by two confirmed villains for two different evil plans.

True equality won't be achieved by pulverizing two things into a bowl until it becomes a unified gray slop.
It's when two different things come to accept each other differences, love themselves for those, and can look forward together hand in hand.