the Plague Hearts are actively evolving at an observable rate.
While it may be one of the more obvious theories in this game, we can see that the plague hearts and blood plague in general are evolving as time goes on. At the game's launch plague hearts were hardly blips on the map, having to be actively searched out for and only really infected the building it stayed in. However as time went on, they turned into a noticeable problem one that became a major issue. They become more common, and in Heartland, we even saw the full scope of what it could do. That's were things took a turn for the worse.Plague Walls cropped up, and from there it was first observed that the blood plague was beginning to effect freak zombies. ultimately the plague walls were destroyed in Trumbull Valley, however the same cannot be said for other places. Plague hearts from then on only became more dangerous. They now infected entire areas around them, making it unsafe to put up outposts. Blood freaks became a common sight in more hostile regions, and most recently, they've even began taking control of hordes and infestations.
From a gameplay standpoint this is all to spruce up the game and keep it dynamic and fun, however it's not out of the question that at the same time, we as players are actively experiencing the evolution and advancement of plague hearts.
The Plague is a massive depopulation plot from the U.S. government
Believing that Earth could no longer support the current population, the government or some faction within the government intentionally engineered the Plague to wipe out the vast majority of mankind. This is why the U.S. military is so quick to abandon survivors, as everyone dying is intended. Project Osiris is meant to set up a secure bunker for the nation's VIPs to wait out the apocalypse before coming back in force to retake the Earth. The Plague Hearts are engineered (or perhaps even programmed) specifically to prevent large survivor communities from emerging and challenging the U.S. government, which is why they are so intelligent. Red Talon is the Big Good
The whole talk about them running a labor camp is just slander from the Network. Red Talon is way too generous to survivor communities in actual gameplay to be as ruthless as the Network paints them to be. Red Talon is a lot worse than they seem to be.
There are multiple hints and nods a player can find throughout the game that Red Talon may be up to much more sinister activities than just fighting back the zombies. From Chavez being really dodgy as to why he left Red Talon, and a note you can find on a dead Red Talon agent has a chance to be a suicide note talking about how they can't stop envisioning what they saw at Camp Eerie.