Sorry it took me so long to write this - it's been on my mind for a while, and I've been asked about it several times, but there's a lot to consider. The books raise a lot of interesting questions which have no obvious correct answer.
If anyone reading this post hasn't read them, they provide excellent food for thought, regardless of your personal beliefs, and I highly recommend them as reading to anyone with the slightest interest. The God Delusion might be a better one to start with if you are not American, or if you are wondering about what reasons exist for atheism, but I imagine many of the points in Letter to a Christian Nation are relevent outside the US as well, especially because of the large role that this country which is increasingly run by religious extremists plays on the international stage, and it's short enough that you could read it in a couple of hours if you don't have time for a long book. Regardless of your beliefs, you should never fear to read a book on the basis of what it might say, and you should always try to understand why it is that you believe what you believe.
Finally, my apologies for the extremely long post, but as I said, there's a lot to think about. I wouldn't be surprised if Ubuntu is the only person who reads this, but I hope at least he (she?) will read it in its entirety, and maybe a few others will as well.
My Thoughts on The God Delusion and Letter to a Christian Nation
In The God Delusion, Richard Dawkins proposes a thesis: "There is a personal god who answers prayers and performs miracles." He then is dismisses this thesis with the level of rigor well beyond what one might expect from any scientific rebuttal of a proposed theory. He then goes on to show that religion as a whole causes much more harm than good. He gives plenty of evidence for this thesis, and it is probably true, although I'm sure it would be very hard to quantify exactly what good comes about because of religion, and what harm comes about, and relate the two.
However, he never proves his alternative thesis "there is no god". He brings up the point that without knowing which of two mutually exclusive and exhaustive possibilities is correct, we can nevertheless judge their relative likelihoods of being correct. This is certainly true. He then says that there not being a god is much more likely than there being a god. I happen to agree with him on this issue, but he doesn't provide any convincing objective grounds to conclude that this is true, so he has no right to say that his position is logical, but the idea that there is a god is not. However, if you include, together with the idea that there is a god, the further idea that this god acts to perform miracles in the world, perhaps during the present, and at least within recorded history, this belief can be objectively dismissed due to lack of evidence, and due to a great deal of evidence that claimed miracles are not the product of divine intervention, and due to the very clear propensity of humans to see supernatural actors present when there is only coincidence and natural forces at work.
Sam Harris doesn't go into the same detail as Dawkins in discussing reasons to believe or not believe in god (in Letter to a Christian Nation - I imagine he does discuss them in The End of Faith, and he clearly agrees with Dawkins on a great many things). He does talk a lot about the harm done by religious beliefs, particularly those of the conservative Christian movement in the United States. I certainly agree with him in his analysis of the problems with the conservative Christian movement. One of my good friends from college is one of the nicest and most moral people I know, but because of his religion, he believes homosexuality to be an immoral act. I'm not sure in what regards this has affected his actions, but this belief has caused an otherwise good person to see many people who never did anything to harm anyone as immoral. This is enough of a problem in and of itself, but when such people gain political power, it can cause even good people to intentionally pass laws infringing upon the rights of moral members of society. Nobel Prize-winning physicist Steven Weinberg was surely correct when he described the single most damaging result of religion: "Without it you'd have good people doing good things and evil people doing evil things. But for good people to do evil things, it takes religion."
However, the idea that some religions are much more problematic than others is completely ignored by both books, except in the cases where Harris and Dawkins say that a religion should not be viewed as a religion at all, but is a philosophy instead (Buddhism, for example). However, it's an important distinction to make because they are broadly indicting all religions, despite the fact that some religions do no harm at all, and may even provide overall benefit. Letter is much more specifically about a specific brand of a specific religion which does do a lot of harm, and I completely agree with its comments in regard to that religion, and Delusion is mainly about a similar set of beliefs, but they both make it clear that the problem, in their opinion, is with all belief that does not have a solid basis in fact. To me, there are two real problems with most religions, and neither are the mere fact of belief in the supernatural. The first is the idea that we should believe something which is not only unsupported by evidence, but also contrary to available evidence: for example, disbelieving evolution despite the vast amount of evidence that has been accumulated. The second is the idea that there is a god-given moral code which trumps all others. These two things are the real cause of all the harm that religion is responsible for, because this in particular is what causes good people to do evil things.
(In addition to good people doing bad things, Dawkins also blames religion for the evil that is responsible for inter-group warfare when there is nothing to label the different groups by besides religion, but this strikes me as terribly unfair because religion is no more responsible for that then skin color is responsible for inter-group warfare between groups of different skin color - one might as well say that skin is evil because if we were all skinless, nobody would be treated differently on the basis of skin color.)
On the subject of a moral code, Dawkins and Harris also seem to have arrived at a single correct moral code which trumps all others based on the idea of suffering. This is surely a better basis for a moral code than religion, since instead of taking a book that some (not especially moral) people wrote two thousand years ago in a very type of world than the world of today, they try to use the golden rule and the idea of suffering as moral guidelines, which is at least logical. However, they make no case at all that it is the right way to determine morality, and I don't think it is. For example, suppose I find out that the person living in the apartment next to me is chronically depressed, suffers from back pain, and has no friends or family. I then decide to break into his apartment, kill him, and take all his stuff. What suffering have I caused? Certainly my actions are not in any way moral, and I'm not claiming that Dawkins or Harris would think they are, but it does call into question to what extent suffering should be used as the basis for morality. Certainly it should be a consideration, but it can't be the only consideration either.
Dawkins and Harris conclude that there is no god, and I agree. They also say that the idea that there is a personal god who performs miracles can be conclusively shown to be false, and I agree there as well, so I would say that believing in a personal god who performs miracles indicates either irrationality or ignorance of the available evidence. However, since there is no proof of the nonexistence of a noninterventionist god who has had no effect on the universe since the big bang (which god may or may not have caused), I don't think that this belief can be fairly said to be either irrational or ignorant. Dawkins and Harris conclude that religion is by its very nature harmful. I disagree there, but I do think that any religion which claims that there is a god-given moral code which is the source of all morality is harmful, and also the idea that we should believe things which are contrary to known evidence is harmful. I have no problem with any religion which is not guilty of either of these things.
Dawkins and Harris are mostly silent on the issue of what should be done about the problem of the existence of religions which do do these things, which is understandable, as there is no easy answer. I agree that such beliefs should be called into question, and a national and international debate on the subject should be opened. I think this will do little to spread atheism besides converting a few fence sitters, but perhaps as children grow up in a society where "the god delusion" is openly debated, they will be less vulnerable to dogma, and in any case it might spread understanding and tolerance of atheism, and allow atheists to be more comfortable and open with their beliefs. I have never denied that I am an atheist, but I have also often been reluctant to publicize it, so while I'm certainly not in the atheist closet, I'm not exactly out of it either. I plan to teach, and I am painfully aware of the fact that certain institutions may be leery of the potential influence an atheist teacher may exert, and I do not intend to go out of my way to minimize that influence. Since I hope to teach at the college level, I imagine that this will not be an issue, but I do recognize its potential to become one depending on where I want to teach.
One final word-
My thoughts on many of these subjects are still evolving. I sometimes change my mind completely, but I generally keep returning to basically the viewpoint I've expressed here. To me, the most important questions are how much harm do specific beliefs do, and how can you reduce the number of people who hold harmful beliefs without doing harm in the process.