Why are there atheists? Saying you're an atheist merely tells people you don't believe in any god or gods. So why say it at all? And why, somebody asked today, are there no aleprechaunists, fiercely claiming that leprechauns do not exist?

Here's why, in a comment I just posted in response to a video by someone asking exactly that kind of question:

If people believed in leprechauns and went around trying to convert you to their ridiculous deity God O'Murphy, ostracised you if you didn't believe in the pot of gold, and wanted to put giant pictures of shamrocks in schools and courthouses, I guarantee you there would be aleprechaunists. As nobody believes in leprechauns, you'll instead find atheists, speaking out when your equally silly beliefs in God contradict and contend with their lives and notion of what is real.

Sometimes YouTube's 500-character limit is just about enough to say all you need to say.