If I tell someone I'm a libertarian, the predominant response I get is, "whats that?", then I explain it to them.
If I tell someone I'm a libertarian and they say, "oh like glenn beck", I'll say, no, not like glenn beck, then I explain it to them, problem solved.
If I start using Voluntaryist or some such shit, all I'm going to get is a bunch more people saying, "whats that?", and if anyone famous ever starts using it, and they don't use it in the same way as I'm using it, I'll have to switch name again to avoid "mislabeling".
God is a perfect example. Some people say god is love. Some people say god is math and physics. Some people think god is a big beardy fuck sitting in the sky. It would be impossible to keep track of all the different names needed for all the billions of definitions of god.
So if someone says, I believe in god, all I have to say is "what do you mean by that?". Definition problem solved. Everyone doesnt need to invent a separate definition for their own quirk. Its accepted in language that people use words in different ways to other people.
Also, the difference between atheism and saying there is no god is simple.
I don't believe in unicorns. - (lack of belief)
I believe there are no unicorns. - (belief in a lack)