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.
There’s a lot to unpack. Let’s start off with morality.
Regardless of whether there is or is not an afterlife, morality exists. We make moral decisions and do our best to construct and explain moral frameworks. We are all driven - to a greater or lesser extent by concepts of good and bad, moral and immoral.
Whether or not our actions truly matter on a universal scale; or to some external diety - does not change the fact that it still matters to us.
In the framework of atheism, the stars don’t give a sh*t if the earth winks out tomorrow. If races are wiped out, if we all suffer and die, or if transgender girls are able to use the wrong bathroom. But we ourselves still remain moral creatures and it matters to us.
In this respect - the lack of an afterlife doesn’t mean that morality “doesn’t matter”, it simply constrains who it matters to, to humans.
Contrast this to a typical afterlife. If someone is looking forward to some infinitely positive reward in heaven - does their suffering in this world really matter that much?
If our life is a mere blip - a nothing : just a test as a prelude to a real reward - does our doing anything beyond the minimum necessary to secure paradise actually matter? Obviously not.
Likewise, we are here for a few short Years - 100 tops. This is the only life we get. It is our only chance. I every one of our decisions at every point matters as a result.
At its most basic level - in a world without god, where thus earth is not just the preliminary test for a world that matters, what we do is all we have, our choices are the most important we will ever make.
