I view this the same as being born human. We, collectively as a race, agree for the good of the general community that it's not nice to kill people. We may not have officially agreed to those terms, but that won't stop the police from knocking if you go and kill someone.
I don't know how to exactly tell you, this but you've just managed to fail history and logic forever with this statement. While it's generally been accepted that we shouldn't kill the people that we're living around, "tribes" of people have been pretty much okay with killing as long as it's not likely to affect them.
http://en.wikipedia.org/wiki/Age_of_majority suggests that most of the nations on earth have a point at which you officially agree to the terms that are imposed by the law. That is why the police are allowed to show up. And why Eloraam is allowed to do what she chooses to.
Joining a community doesn't require that you better it, It only requires that you interact with it. If you choose not to better said community, it's wise to limit the effects of your interactions.