atheism self-refuting?

here's something I came across reading Zacharias… i’l l try to put it in more rigorous form:

1. Atheism is the positive assertion of God’s non-existence.
2. The positive assertion of God’s non-existence is an absolute negation.
3. Making an absolute negation requires infinite knowledge.
4. Only God has infinite knowledge.
5. Thus, infinite knowledge is required to make the assertion that there is no Being with infinite knowledge, and thus atheism is false. (this does not imply that theism is true, btw.)

well, though it sounds promising, I have some reservations abt this argument. maybe there is a weak link in point 3. what do you guys think?

[edit: I think point 3 is very questionable and point 2 as well. Suppose God tells me that there are no unicorns. Since I believe in God's testimony, I make the positive assertion of the non-existence of unicorns. Either that is an absolute negation or it is not. If it is, then obviously point 3 is false, since I don't need infinite knowledge to make that assertion. If it is not an absolute negation, then why should the positive assertion of God's non-existence be an absolute negation?

Thus, it is not surprising that this argument isn't convincing.]