Actually, it's you playing the game here. The thread is comparing the ethics of humanism with those ascribed to God, which I take to mean the god of the Christian Bible. That's a proper comparison.
When you transform "humanism" into "athiesm" and compare that to Christianity, you're making a category error. You need to compare atheism to theism, or a particular atheistic ideology to a particular religion. By switching from humanism to atheism, you bring in ideologies with are antithetical to humanism and repudiated by it, yet you want to hang that on humanists using this category trick of yours.
You objected that "atheists like yourself should not be considered as having any dirty hands from this." Of course we do, just as theist like yourself should object to my blaming Christian theists for the barbarism of the Aztecs who pulled beating hearts out of victims or islanders that throw virgin girls into burning volcanoes.
All that we humanists have in common with the Communist dictators is atheism, and probably aleprechaunism and avampirism as well. What we both don't believe doesn't really make us kindred spirits.
Those totalitarian regimes have much more in common with religions like Christianity than secular humanism. They just substitute a man for the god, who issues commandments without giving reasons, doesn't debate or negotiate them, and expects complete submission and obedience under threat of retributive punishment. Sound familiar? Jehovah and Stalin have all of that in common.
So I give those Communist regimes back to you authoritarians. We're the freedom ideology, the one that respects the dignity of man, celebrates his accomplishments and potential, and wants him to be all that he can be: free, well educated, autonomous, citizens living in a just society, each free to pursue happiness as he envisions it within the limits of a just and rational body of law intended to safeguard those same opportunities for others, laws that citizens write together when selected by other citizen to do that job.
You won't find those humanist ideals in Stalinism or in the Christian Bible:
"The problem with fascism and communism, however, is not that they are too critical of religion. The problem is that they are too much like religions. Such regimes are dogmatic to the core and generally give rise to personality cults that are indistinguishable from cults of religious hero worship.- Sam Harris