Well, I think
weak atheism makes a lot of sense. If one has personally investigated a religion and found that the evidence specifically indicates the falsehood of it, disbelieving in that deity is a rational endeavor. Alternatively, if one already knows something to be true which prevents a specific religion from being true, one may rationally disbelieve in it. Indeed, as a
Muslim, I am effectively an atheist towards deities other than
God. This is the essence of weak atheism.
Specific gods do not exist. This is the essence, then of my theism, and, I suspect of the theism of most of humanity.
It is perhaps a bit more of a stretch to be a strong atheist, a position which implies a type of faith upon the holder as they have faith that the universe is material and nothing else. I think weak atheism is the most logical position one who does not have a religion can take, though I cannot completely dismiss strong atheism, either. I simply disagree with the unproven assertion, the non-existence of what we Muslims refer to as the unseen.
Any logical system must begin with some postulate which is taken axiomatically. Now, the Qur'an is that postulate for me, which was established through an epiphany. As such, I can only offer it to the unbeliever as the starting point. If God does not lead them to that truth, then certainly I cannot. If they are sincere in their search for the truth, God will not abandon them, even if he does not lead them to Islam right now. The Qur'an calls itself a reminder. This is the manner in which my epiphany worked. I was a weak atheist at the time (as I had been, without the knowledge of my parents, since I was fifteen), and, believe me, the last thing I wanted to do was believe in God. I was happy, and pretty content. I was not known as a bad guy, though I indulged in the normal sins of the day. One of the things I did enjoy, however, was attacking weak logical positions, and those can be found everywhere. Politics and religion seemed to be the most common areas, however. I used to point out to people where the flaws in their logic was found regarding those two matters. I didn't attack, say the Bible, on the basis of what it said, rather I attacked the position of the speaker based upon the statements of the Bible, if that was what they believed in, or libertarianism, if that is what they believed in, or Objectivism, if that was what they believed in, and so on. I encountered Islam, and honestly was just looking to have a little fun attacking weak positions. In order for me to do that, however, I would need to know a bit about the Qur'an and other primary sources of Islamic theology. I started reading a translation of the Qur'an online and investigating Muslim claims. Within a few months, I was a Muslim. I don't believe I abandoned my rationality at any time during this time. Rather, the axioms upon which that rationality is founded were amended alhamdulilah.
So really, one might actually ask the question, How can a thinking, rational adult not be an atheist?. If one is an agnostic, in the absolute sense, this indicates a lack of investigation. I can't believe you haven't found a single diety which can't be effectively disproven. Heck, even Zeus would count for that. Strong atheism is another type of faith in and of itself, namely, that the universe is material and no gods of any sort, whether or not I have encountered the claims of them, exist. Agnosticism towards those which cannot be effectively falsified is quite reasonable, and is what I suspect, most agnostics mean when they describe themselves as an agnostic. I'll bet just about all of them disbelieve in Jim Jones.:)