Atheism = self defeating.
First may we define our terms. The word Atheism comes literally from the Greek, alpha the negative and theos [for God], therefore “negative God” or there is no God. It is not saying, “I do not think or believe there is a God”, rather it affirms the non existence of God. It affirms a negative in the absolute. Anyone who took philosophy 101 knows you cannot affirm a negative in the absolute. It is a logical contradiction. Therefore it is self defeating. It also breaks the rule of non contradiction by ascribing to itself a divine attribute while at the same time denying the existence of the Divine. Atheism not only denounces the existence of God, but by its own definition denounces the principle by which it criticizes the reality of God. To make an absolute statement in the negative is similar to saying that nowhere in the universe does there exist a flying spaghetti monster. For the atheist to make such a claim he must have unlimited knowledge of this universe. What the atheist is fundamentally saying is that he has infinite knowledge of this universe to affirm that there exist no being with infinite knowledge. It is self defeating.
Good use of logic. However, as you are aware from your philosophy 101 class, a logical argument has be based upon true premises. Your premise (that atheism means 'negative god' which should be applied today) is false for the following three reasons. (After taking your philosophy 101 class you should be aware that if any one of the following three statements is true then your premise is false, meaning that your conclusion of atheism being self defeating is also false.)
1) The word atheism (atheos) in Greek means 'without god(s)' or 'without deities', not negative god as you presume. Early Christians in Greece were called atheists by the populous for their lack of belief in many gods. So you see the early literal meaning of the word is neither 'negative god', nor 'affirms the negative in the absolute'.
2) Basing a modern linguistic meaning on the 500 BC Greek use of a word is preposterous, as atheism has its roots in 600 BC India.
3) To get to where we are today we have had to pass through classical antiquity and the enlightenment. The meaning of words change in time, all of your language has - you would not base the meaning of all of your words used today on what they meant 2,500 years ago, that would be absurd.
On this point, your philosophy 101 class may have taught you something about Socrates. Please read Plato's dialogue of Cratylus (your philosophy 101 teacher may or may not be aware of it, ask him/her).
Socrates is brought in to help with an answer to an argument between Heraclitus and Cratylus. The former argued that names of words are posited by custom and convention, whereas Cratylus (like you) argues that names of words have some sort of natural meaning attached to them. After listening to both arguments Socrates describes the creation of words as being like an artist who expresses the essence of his subject in the painting. Over time the meaning of the names of words change, like the creation of the picture from the first use of the artists brush. He states, "names have been so twisted in all manner of ways, that I should not be surprised if the old language when compared with that now in use would appear to us to be a barbarous tongue."
Finally, Socrates concludes that the study of language to gauge a useful meaning is philosophically inferior to the study of the things themselves.
Take Socrates advice - to gauge a philosophical understanding of a topic study its things, not its words.
I rather suspect that the use of literal Greek for gauging some sort of modern day meaning is influenced by your JW days. Get out of the box and move on, there is big wide world out there.