Regarding the sudden ramping up in violence on the part of the Vox Populi after stepping through that tear, could it be a result of the fact that Booker was a leader and a martyr to them in that specific iteration?
As mentioned in the podcast, Booker is not a nice dude, and it seems as though he's never a met a problem he couldn't solve by murdering it. That the Vox would take cues from him once he demonstrated how effective brutality is, isn't all that surprising. Did anyone in the game talk about scalping other than Booker/Comstock? Yet during the Vox rebellion, there's a board with the scalps of the Founders pinned up for all to see. Which isn't to say that Fitzroy doesn't have her own violent streak. There's a few voxophones where she compares herself to a fire, ravaging through Columbia.
"When you forced deep underground, well-- you see things from the bottom up. And down at the bottom of the city, I saw a fire burning. A fire's got heat aplenty, but it ain't got no mouth. Daisy...now, she got herself a mouth big enough for all the fires in Columbia.
"You ever see a forest at the beginning of a fire? Before the first flame, you see them possums and squirrels, running through the trees. They know what?s coming. But the fat bears with their bellies full a? honey, well -- you can?t hardly wake them up from their comfortable hibernation. We?re going to Emporia. And then, we gon? see what it takes to rouse them from their slumber."
It's interesting that Fitzroy is Infinite's parallel to Atlas/Fontaine. Both begin the revolution that leads to the downfall of their respective cities. Both are originally presented as allies, promising escape in exchange for assistance. Both betray the protagonist and are further corrupted by their success. Fitzroy ends up stabbed to death by Elizabeth, while Atlas is swarmed by little sisters repeatedly stabbing him with their syringes.