On the other hand, atheism can be defined not not by the non-belief in powerful non-human beings, but in the non-belief in the right of these beings, by virtue of their very nature, to receive worship.
The claim that anyone or anything can have rights due to its nature alone, rather than based on his utilitarian value or his ability to punish or reward, is probably less popular today than it was in the ancient world, but it has not disappeared entirely. Most people will agree that a child has a right to food, clothing, shelter, medicine, and even education, however inconvenient that might be and whether or not the person (or even society) supplying these benefits gets anything in return. Most people think that each person has a right to a fair trial before punishment, a right not to be enslaved, etc. There has always been a feeling that gods have a similar right to worship -- as distinct from human despots like those of the Kim dynasty in North Korea, who often demand worship.
It seems fair to say that modern atheism has more to do with the second point than with the first. First of all, modern atheists are apt to think it likely that not only are there other intelligent beings in the universe, but that many of them may be so technologically advanced that they could do things that would seem completely impossible to us. Secondly, atheists tend to believe that the ultimate Theory of Everything in physics is one, simple (in a sense), and beautiful (in a sense); Christians may agree, on the basis of God's creation reflecting God's nature, but atheists make the TOE into a kind of Ersatz God. Christians say that God is uncreated and responsible for the reality of everything else; atheists say the TOE is uncreated and responsible for everything else. Modern atheists basically acknowledge a pantheistic god who makes no moral demands, and they occasionally like to celebrate the glories of this god (like Carl Sagan did in the "Missa Gaia" in 1993) in quasi-religious ways, but truly and fundamentally they refuse to worship it.
No doubt there are some exceptions, but practically all modern atheists are moral relativists. In other words, they would deny that conscience (contrary to, for example, Budziszewski) is a perception of an objective, external, non-physical reality. On the contrary, they understand conscience as preferences based on (biological, not metaphysical) nature and nurture. They might paraphrase Yoda: "Do. Or do not. There is no good or evil."
The odd thing is that someone who truly embraces these ideas has no imperative to share them. He might feel an irrational desire to share them, or he might share them in order to try to induce people to behave in a desired way. Then again, he might find it more useful to pretend to be the prophet of a god in whom he does not believe. Look at how many cults -- including cult-like organizations like the Legion of Christ under Marcial Maciel -- end up being schemes to provide the leaders with sex and money; is it really plausible that these leaders truly believe in God? But if there really is no God and no real right or wrong, it is more rational to be a cult leader than to be an evangelist of atheism.