Was what Carol did really that "dark"? She was trying to prevent a plague.
That's why the people were contained in A-Block/Death Row. To prevent the spread of the illness.
And yes what she did was dark considering she killed two living people not posing a meaningful threat. What she did with the bodies is another discussion, but she still killed to living/non-walker people who were contained. That's pretty damn dark.
Along another line... It's a common TV/movie trope to do this but covering your mouth/nose with a mask or cloth doesn't do anything to protect the wearer. If you can breathe through it you can breathe in germs/viruses/bacteria given that those things are aerosolized in air molecules which your mask is porous too. Wearing mask protects OTHERS from YOUR germs, coughs, spittle because the mask can contain those things (aerosolized germs and such being much more contained just off the mouth than in open air.)
So, really, everyone wearing a covering in the episode isn't doing themselves too much good. No harm, sure, (and it's is SOME protection from flying spittle/blood) but it's not a 100% defense from germs and viruses in the air.
Is it me or did this episode step down the aggressiveness of the virus?
In the first episode Patrick goes from "not feeling well" to cough up blood and dying within a few hours. Right now it seems everyone is sort of managing the virus a bit better.