Theists often ask me why I care so much about something I don't believe in. When I first started openly questioning religion, I couldn't answer that question. I knew why, but I just couldn't put it into words yet. The reason is because the claims and actions of theists can be harmful to people, on a psychological and physical level. I don't refute the claims of Bigfoot sightings because while I don't believe in them, I also don't believe that other people believing in Bigfoot will have a negative effect on society in general, or even that person specifically. A belief in god can have profound effects on one's actions and thoughts, cognitive dissonance notwithstanding.
All of that is well and good, but why does this community of people need to have their own label? The only reason there is a need to call attention to the fact that we haven't been convinced there is a god is because there are people out there trying to convince others there is a god. I can't speak for anyone else, but I didn't wake up one day and decide to boycott God Inc.. I don't hate god, the same way I don't hate Bigfoot.
When I really think about it, I can understand why some theists might think atheism is this group that dissenters join when they are mad at god, or if they don't want to be responsible for their actions, allowing them to “live it up” with a clear conscience. Sometimes I hear some atheists speak as if they are speaking for atheists everywhere, and while it bothers me slightly because speaking on behalf of a group indicates that everyone in the group thinks the same way, and possibly because there is a doctrine that says they have to, I can't be too mad because usually atheists only speak in those kinds of terms for wholly accepted truths. The only example I can think of is when atheists tell theists that the only thing that all atheists have in common is that we don't believe in god.
The label of atheist is a necessity in my mind, and will continue to be until we reach a point where religions like Christianity are taken as seriously as religions like Scientology, and I don't see that day arriving anytime soon.