Atheists r supposed to b humanists, but sadly we don't see eye to eye on so many world and current issues. Israel and Palestine, immigration in America , abortion , socialism and communism as against free market capitalism and its monoply stage imperialism, American domination and occupation , sovereignty of nations and their decision to chart their own course without intervention and economic blockade and pressures climate change ,etc etc.
I don't know that atheists are supposed to be humanists. I am an atheist and probably not at all a humanist. Humanism can and does include religious people, and in the West was largely an outgrowth of Christianity. Early humanists included the likes of St. Thomas More, author of Utopia who just happens to be one of my direct ancestors and a staunch catholic.
Why do you feel our one area of more-or-less agreement, no deities, would make us likely to agree on anything else!? The hallmark of an atheist is Thinking Things Through......nobody thinks the same as everybody else!