I think what some people are missing here is that one of the core themes of this episode is the idea that what is "right" and what is "necessary" aren't always the same thing. To my mind, that realisation is the reason why Tyreese forgave Carol. He recognised that what she did was necessary and they live in a world where doing what is "right" is a luxury they can't always afford.
It's a fine line to walk of course, since doing what is right can easily be forgotten about altogether. At which point we cease being human and go back to being animals who act purely on survival instincts. On the other hand doing what is right at the expense of necessities is a negative survival trait and an easy shortcut to extinction.