Two I can think of. One is that secular humanists tend to associate
mortality with atheism and immortality with theism. The other is that
most secular humanists I know tend to reject religious metaphysics
-- i.e., they don't believe in a Creator or supernatural realm -- but, for
the most part, accept JudeoChristian morality -- at least the parts
dealing with social ethics. (Many people also conflate ethics with
social ethics too, but this goes beyond humanism per se.)
Daniel Ust