this for starters. (Everybody should read it anyway. It's a wonderful essay.) I suppose it's possible that you literally do not know that you are talking nonsense.
Humanism as a movement was grounded in the rediscovery of classical culture during the Renaissance -- a classical culture that predated Christianity by four centuries, had almost no contact with Mosaic culture, and was remarkable in being relatively free of supernatural superstitions, particularly in its fullest development. Western humanism is so far from being grounded in theism in general or Christianity in particular that indeed it grew up in large part in defiance of Christianity's brutality and pretensions to being the single path towards human fulfillment. I won't play your "yay team!" game and claim that humanism is grounded in atheism because I believe humanism can grow alongside any type of faith or none at all -- they are not relevant to each other -- but if I did I'd have more evidence on my side than do you.
Please stick to talking about religion. When you talk about atheism you embarrass yourself.