It isn't fixed when found, because the people doing it are the people responsible for fixing it, and the people it's done to have a hard time reaching the King, who currently is the only neutral overseer.
Their allies own slaves so obviously it occurs to the people, it's just distasteful, which pushes people to think of half-exiles as "obviously being different!!"
At its worst, half-exiles are "cared for" in much the same way that an intelligent owner cares for their slaves - feeding them well and tending to their wounds so they can work harder. Obviously the interactions with shamans started from both necessity and the thought that this would cleanse them of corruption faster, but, in the north, it has by all appearances gradually changed to something different.
They do not contradict each other: one is the fact that half-exiles can be from any group the other is the fact that half-exiles are disproportionately from racial minorities and that this is being deliberately perpetuated, largely by the provinces in the north. Both of these are literal WoG facts, as I quoted earlier.
The vote is for occupation, i.e. Masons, farmers, etc. I see no reason why people who are believed to be spiritually corrupt (albeit theoretically temporarily) would be given much of a voice, especially if it's in the best interests of the people in power for this not to occur. Note that the occupational guilds will be divided geographically, such that members possessing certain dispositions toward the issue of half-exiles will be the ones in power where the issue is occurring the most outrageously. As noted in the quotes, people, especially half-exiles, rarely leave their village and thus communication and collaboration between different groups of half-exiles in order to push for an overarching representative body for their "occupation" is unlikely to occur.