The word "atheist" often does not reflect the actions of people who call themselves such. Atheist means "without God" etymologically, but most atheists seem more interested in debunking the doctrines of religion, doctrines which are only man's idea of what God and Heaven might be like.
In its Greek roots, the word atheist breaks down into:
a: which is prefix meaning "without" or "not"
theós: meaning "deity" or "god"
But when you look at the arguments of atheist online, their focus is on countering or debunking the doctrines religion, rather than directly attempting to counter the possibility of a Heaven in which God resides, and the survival of consciousness after death in this heavenly environment.
In this respect, an atheist might better be described as athreskos (to coin a term), which in its Greek roots, breaks down into:
a: which is prefix meaning "without" or "not"
thréskeia: which is the closest term the ancient Greeks had for religion.
So most atheists might in practice be athreskoi (the plural of athreskos) — people who do not believe in the doctrines of religion.
It might be argued that athreskeia (my term meaning the philosophy which opposes the doctrines of religion) plays an important role in the world, by exposing religion for a manmade set of ideas about God and Heaven (as opposed to the truth about God and Heaven, if this can be known).
But then atheists should make their position clear: that they are against manmade concepts of God and Heaven found within religion.
Interestingly, individuals who say they have direct knowledge of Heaven though a near-death experience (NDE) often also end up opposing religious doctrines, as their heavenly experience does not line up with what religions teach. So these people might also be accurately described as athreskoi, along with many atheists.