I had this same argument in a thread about a month ago. It IS entirely semantics.
Of course babies don't believe in God. The commonest usage of the term athiest in our culture, however, refers to rejection of theism.
Not the same thing.
Some people, including many on this forum (CFLarsen, for instance) have a less-commonly understood definition of the term atheist; to mean literally without a belief in God.
Both meanings are valid. I prefer to adopt a label than be born with it, however. I prefer to choose atheism - not to have it thrust upon me by default. I want to earn the title by thinking about the issues involved and making my choice.
Incidentally, my evidence for the assertion that 'rejecting theism' is the usage in common currency comes from a review of available dictionary sources. Before anyone mentions it, I *know* that dictionaries don't define words - but they do provide an insight into the linguistic zeitgeist.