I don't know how anyone can say that what Carol was doing was rational. It was absolutely stupid because of the complete lack of understanding about how disease is transmitted.
Rationality is partially defined by circumstance. It's a world where dead people get up and try to bite living people. Not knowing how
disease is being transmitted is irrelevant if you know for a fact that it is,
somehow, being transmitted, it's fatal, and people who die get up again and try to eat living people. And knowing how disease is ransmitted is still irrelevant in an environment where proper isolation and treatment are impossible.
Carol did what she could with the knowledge she had and the circumstances she was given to work with. .
Rick, the doctor and Hershel know nothing about the disease--or if it will respond to antibiotics
. The one thing everyone knows is that the disease leads to death, and reanimation as a walker. Rick must suffer from some kind of Pollyanna
complex to think Carol is dangerous, when she ended a problem that had only one conclusion.
Rick did not know if the scouting party would return (a common risk in that world), so he's operating off of much assumption, and a truckload of hypocrisy, when we remember his ease with the ending of life in seasons 2 and 3.