Ooh, TREG, you fail. The whole Code Red thing was pretty easy to understand. Really, bizarrely, stupidly easy. This may be the Republican in me talking, but I would have done the exact same thing in that situation.
Think about how fast rage spreads. It's almost instantaneous. No fever and nausua, nothing. You get infected, and you're one of them almost immediately. Because of the epidemiology of the disease, killing everyone in London was the only possible way to to stop it. What were they going to do - evac people and risk spreading Rage to the mainland? They did what they had to do to save the entire frikkin world.
Of course, as we saw, it didn't work. A carrier was evacuated to Paris, and like any good zombie movie ending should imply, was the cause of a literal apocolypse.
I agree that the characters had the intelligence afforded to typical horror fare, but the Code Red situation was absolutely reasonable. Why did they slaughter the uninfected? Because there was no way to save them without endangering the entire world.
(Oh, and nobody really knows what Los Ganados are (Well, nobody knows what Las Plagas are, which control Los Ganados). Maybe we will find out in RE5. Regardless, though, Los Ganados were indeed not zombies. Everyone knows zombies can't talk. People in robes droning "die" in spanish do not zombies make.)