Many people are hesitant to identify as atheists because of the social stigma they may face, making it hard to pinpoint connections and differences among this group.
Secular just means not structured around religion. It makes sense for a democracy to be secular as its constituents come from different religions
Humanism just means finding morality and ethics based on humanitarian ideals instead of from religious doctrine
I am not sure how you think Atheism has anything to do with the above, but yes atheists would be the most likely ones to invoke ideas of secular humanism
Secular just means not structured around religion. It makes sense for a democracy to be secular as its constituents come from different religions
Humanism just means finding morality and ethics based on humanitarian ideals instead of from religious doctrine
I am not sure how you think Atheism has anything to do with the above, but yes atheists would be the most likely ones to invoke ideas of secular humanism