In Red Faction, the miners on Mars are oppressed by Ultor beyond anything. While this can still be said to be part of their policy to exploit their workforce as much as possible, I don't get why they would willingly kill their miners in such great numbers. We learn that the "Plague" is engineered by Capek (Ultor's version of a crazy scientist) and administered to the miners. But why? Why would they willingly make their workforce sick (they cannot work, but cost money) and ultimately kill them (reducing the number of workers)?
The goal is likely to keep morale down. Consider a parallel to coal miners - if you keep them worked so hard they can't group up, sick so they aren't strong enough to resist, and mentally beaten down so they don't want to resist, you can control them entirely until you reach the limit and they break.
You can always hire new people who don't think it is that bad since you control all the means of information leaving the planet. Given the EDF's reaction at the end of the game, they were probably suspicious of Ultor's behavior, but had no real proof.