For the most part, the group has kept themselves from killing each other and other non-zombies, but that has been changing since the members are finding themselves in more danger from other humans as time goes on. Glenn finally took the life of a non-zombie and, as you would expect, did not seem to happy about it.
You can still see the humanity in the group once in a while and that is what keeps the show grounded. They can all go around slicing off the heads of zombies and other people, but that would not be a story line that you could keep up forever.
The Walking Dead Season 6 is one of the most watched on television right now and with only four episodes left to go in the season, there will be a lot of work to bring all of the loose ends together for one big climatic scene that fans are used to seeing.