The infected are discriminated against for multiple reasons. They can infect the people around them, and after their death, their body would become an originium nest that would put everyone around them in immediate danger. Being an infected is generally a death sentence, both literally (as oripathy has 100% mortality rate) and societally: it is associated with losing jobs, disappearing from the public eye, losing positions of power, being on forced exile, and so on and so forth. This case is especially not helped by nations who actively attempt to curb the effects of oripathy by separating the healthy from the infected, such as Great Lungmen.
Through one perspective, this discrimination can be seen as a systematic oppression: in a society where being an infected is frowned upon, all decrees in regards to the infected will therefore be oppressive and defending said decrees will be, by association, defending this oppressive system. In this sense, no one who is not infected will ever understand the pains of being an infected. Since a system is made of whole components and cannot be changed without changing the cogs entirely, the only way to dismantle this discrimination is, then, by dismantling the oppressive system entirely.
Therefore, the Reunion Movement is born as a movement by the infected and for the infected, with the goal being to destroy the oppressive system.