Speculation: RDA reverse engineering spiders mycelium will save pandora, not doom it
At first glance the RDA getting their hands on spiders mycelium seems like a bad thing. Bad enough to almost kill the poor kid if your name is jake sully. If humans can breathe the air without masks the rda will spread across the planet and win right? Wrong.
Firstly for the capabilities of the rda nothing will change. The masks are only an issue when you are far away from a base or vehicle to recharge it but going away from those is a bad idea regardless due to all the wildife wanting to meet you (and also eat you). the only thing that really changes from the rdas perspective is the building costs as they no longer need airtight buildings. And even more humans coming to pandora due to this is also not gonna happen because the main issue for the rda in that regard is not space but transportation
Second, the masks kind of work in the rdas favor. they are like an invisible leash around their employees. its hard to strike for better working conditions when your boss can just flick a switch and have you all suffacate. its even harder to defect from the rda as you will never reach somewhere else without running out of air and dying. without the masks the rdas only leverage will be the workers salary wich is hard to spend on pandora or a gun to the head. The masks are not only a leash around the individua workers but also around the entire pandoran colony. without them they could live without supplies from earth and potentinally become idependent.
Third, the mycelium also grants a kuru. This could be seen as an advantage to the rda as they could use the wildlife for their own goals but it also makes the humans able to, as jake puts it "see" pandora. the bond works both ways and can change individuals. in short, many humans in the rda will see not only the beauty of pandora but also how the rda destroys it. it is also stated in frontiers of pandora that the rda already has issues with defectors to the point of executing people even thinking about it. imagine how many issues they have to control their people now that their strongest leverage is gone and said people "seeing" pandora.
in the end, brigehead could fall not to the na'vi, not to eywa but to their own kind