Is secular humanism a religion?
Humanism is a moral view: it holds that we ought to strive to improve the world, we ought to promote human welfare, we ought to be humane, we ought to respect human dignity.
Some theists disagree. Instead of worrying about the material state of the world, they say, we ought to turn inward and improve our souls; instead of promoting human welfare, we ought to worship the glory of God; instead of practicing humanity, piety; contrary to respecting human dignity, we ought to recognize that we are worms who don't deserve the love of God.
Many theists, of course, hold that the metaphysical belief in God is compatible with the moral vision of humanism. Thus there are Christian humanists and Jewish humanists in addition to secular humanists.
Generic humanism is simply a moral doctrine. Christian humanism, however, combines the humanist ethic with the metaphysical commitments of Christianity. Christian humanism, otherwise known as humanistic Christianity, is thus a religion (or a kind of religion).
Secular humanism combines the humanist ethic with the metaphysical doctrine that God does not exist (or the epistemological doctrine that knowledge of God is moot). Secular humanism thus exhibits both features (1) and (2).
Although secular humanists do not have places of worship (3), many of them do engage in ritual (4). Just as Christians borrowed Christmas from pagans, so too do many secular humanists borrow Christmas from Christians. Such humanists, however, seem to me to be nominal humanists; practicing secular humanists would not celebrate Christmas.
Secular humanists do not regard any book as sacred or even as canonical (5).
Secular humanists have organized for political power, and as a consequence there are recognized leaders within secular humanism (6).