Secular humanism is a contradiction. Here's why(note: I am neither an atheist or a humanist) :
Humanism: puts humans at a prime moral/social/philosophical importance.
Atheism: there is no god, therefore there is no afterlife, therefore nothing you do or think matters at all. There is no moral standpoint, only what you like matters.
Here's the problem: In an atheist worldview, why do humans have to be more important than animals? Why aren't monkeys or rats of prime moral importance? Why of all the animals supposedly generated by blind natural processes do humans have to be of any major moral importance? After all, in atheistic worldview, a very good person who does good things like donating to charities, saving people, being kind to others, has the same fate as an evil man who kills everyone he doesn't like, steals whatever he wants, and has lots of hatred - when they both die, they completely disappear. This is the problem with every atheistic world view that claims to have a strong moral code - like communism.