I'm not sure that I agree with organized atheist groups. In a sense, atheism has become a religion of non-religion. There are atheist out there who look for issues to cause problems. Atheist are supposed to be non believers who live and let live. These days, some seek to attack the religious and make demands of how they should worship. That's wrong. Especially from people who don't believe. The extreme atheist are no better than the extreme Christians.
As to the question in the title of this article, NO, atheist should not broaden their purpose. As I've said, they should have no purpose to begin with. Atheist should defend a person's right to worship as much as they defend a person's right not to worship. Just because a person doesn't believe in God doesn't mean they should have an agenda or movement against God.
A lot of people don't believe in Santa Clause, the Easter Bunny, or the Tooth Fairy, but there is no agenda or movement against them. There is no need, purpose, or point. The same with all this hoopla against Christians and their belief.