We don't call ourselves "aSantaClausists", "aUnicornists" or "afairyists" because the labels aren't important. "Atheist" is an important label.

Consider this:

  • U.S. States do not have laws of the books specifically preventing aUnicornists from holding office
  • Public schools across the country aren't using taxpayer dollars attempting to proselytize the belief in unicorns to students, to specifically prevent them from being aUnicornists
  • Professing a disbelief in unicorns is not grounds for jail sentences in any countries
  • People who disbelieve in unicorns aren't regarded, by the public as large, as much of a distrusted demographic as rapists, because they don't believe in unicorns[1]
For a-theists, on the other hand, do have to deal with the above. Atheists didn't make the label important. Theists did.

Labels are used for important distinctive concepts. While any of the above are true for atheists, the label will remain important.