Man, there's a lot of bad faith and delusional commentary in this manga.
I doubt the Japanese actually use the rhetoric of equality and discrimination to marginalize certain groups of people in Japanese society (reverse racism notwithstanding, but even then the person it's alleged was discriminated against is usually the majority race for reverse racism). Actually, I'm pretty sure no one in their right mind would say the job the characters have is somehow discrimination. The artist is associating a rhetoric with an ulterior motive that the rhetoric can't sanely support, and that it isn't ever used to support.
Added to all of that is the implication that the disabled equivalent to an ideology of racial nationalism (like the black panthers) is a solution to the problem of discrimination. In a world where all land is under the sovereignty of some nation-state or other, nationalist separatism among marginalized groups will lead to swift suppression rather than sympathy. I would think history has shown the merit of integration over separatism, but apparently there are people in the world that still believe separating people is the best way to make people's lives better.
There's a reason you don't hear people talk about discrimination against disabled people much at all in America. It's called the Americans with Disabilities Act (ADA for short), and I would encourage you to look into it. It is arguably the most successful tool yet to remedy discrimination, and I can say as a disabled person that it has only made my life better. I certainly don't fear that "SJWs" will call for the elimination of such a remedy because it is "discriminatory against disabled people." You'd have to be out of your mind to suggest something like that, let alone to call your suggestion social justice.