Fauna, including bears and wolves, is trying to kill you, radiation, that's ever-present, is trying to kill you, zombies, in a multitude of colors, are trying to kill you, other players on the server, equipped with guns, are most definitely trying to kill you, and you, yourself, if you don't find food, will die.

While there's obviously potential for working together with other players towards achieving certain goals, the more likely scenario is someone trying to kill you to get your stuff. Or even worse, deceiving you in working together to achieve a particularly difficult goal only to stab you in the back when you're not needed anymore. It's easier to take stuff from someone else than gather it yourself. And since your base is a the perfect bullseye to other players, there is constant threat of griefing.

Because you can build your base that you respawn back to when killed, losing only what you had on you at the time of death, it allows getting back to where you left off quickly.

If worrying that another player might kill you and loot your corpse is not your thing, or if you don't want to deal with someone constantly harassing your base, there are servers available that take away the risk of other player's malicious behavior.