Informed atheism is a rebellion. Not against God, for you don't rebel against things you treat as nonexistant. It's the expression of a rebellion against a popular view that it's ok to hold a belief that you can't demonstrate as true.
There's simple atheism: just failing to believe in a god for whatever reason: you've never been introduced to the concept; you're "angry" at your concept of god; you simply don't have a reason to believe. These are fine; I welcome the day when nearly everyone is a "simple atheist". These are the atheists that hardly need it as a label.
Informed atheism is a different animal: it's the statement that the existence of a god has been almost entirely excluded from belief by our knowledge. We understand there may be flaws in our knowledge, but the number of flaws necessary to allow a god to be real is staggering.
In short, a simple atheist may be easily turned into a believer - indeed, it's happened at least once to every single religious believer - but an informed atheist is