The idea is survival lol, you all have a common enemy which is the zombies but theres no rule on how you treat other players, such as in DayZ because of permadeath people will hesitate to interact with other players, worried, like you would in the real world if it was a zombie apocalypse, that the person youre about to engage may want to double cross you for your items
Stuff like shooting in a town with a loud rifle will piss off other players who are nearby hiding because the whole point of the game isnt about whos the best shooter or whatever, its about who can stay alive and whos smart, which is something very appealing to me