How is it that almost anything that any religious preacher says to prove the existence of God turns out to be typical examples of one or the other of the well known logical fallacies? How is it that they don't realise this simple fact when all such fallacies are enumerated in the Web in such sites as the Wikipedia? Are human being basically very irrational creatures ?

The matter is more complicated than looking at Wikipedia. There are plenty of good reasons for being an atheist, but as I have sought to make evident in replying to other questions in the category of 'religion' there is a vast philosophical literature supporting religious beliefs without what might be called Wikipedia fallacies. You might check out the free online Stanford Encyclopedia of Philosophy entries Philosophy of Religion and, as an example, the entry for the Cosmological Argument, which contains a pretty plausable (non-fallacious) version of the cosmological argument. Check out, too, the Blackwell Companion to Philosophy of Religion. I might also suggest that no philosopher today (or almost none) thinks that they can prove God's existence or non-existence or prove utilitarianism is correct or physicalism or realism in philosophy of science. Today, most of us deal with arguments we take to be plausable or persuasive, but these fall short of proofs.

just to supplement Charles's very fine response: first, yes human beings are very irrational, but you can find irrational humans in every domain, theist and atheist ... if you're looking for 'rationality,' or at least approximations thereof, or at least 'reasonableness,' you probably don't want to be listening to local preachers (or even local 'atheists', whatever that means) -- you want to be talking to more philosophically inclined people (which is more or less what Charles is getting at) -- and there are plenty of deep, engaging, provocative things to think about, with respect to religion -- not merely the existence of God but many related topics -- even when you constrain yourself to trying to be 'rational' ... (I've tried to collect a number of these in my recent book 'The God Question,' which presents what a lot of famous philosophers have said on the subject of religion ...)

hope that's helpful -- best,

AP

Read another response by Charles Taliaferro, Andrew Pessin
Read another response about Rationality, Religion