One interesting claim made by Sam Harris in The Moral Landscape: How Science Can Determine Human Values is that religious values are fundamentally driven by concerns about how circumstances will affect the lives of human beings. For instance, doing what is necessary to get into heaven and avoid hell is ultimately good for you as an individual, even if it involves difficulty and sacrifice during your lifetimes. Similarly, Harris argues that suicide bombers who are partially motivated by the promise of a lavish afterlife are making decisions on the basis of faulty information about how their actions will affect their lives and (possibly) those of others.
Religious believers are arguably trying to maximize human welfare in both this world and the afterlife, which changes their moral calculations:
Religious believers can, therefore, assert the immorality of contraception, masturbation, homosexuality, etc., without ever feeling obliged to argue that these practices actually cause suffering. They can also pursue aims that are flagrantly immoral, in that they needlessly perpetuate human misery, while believing that these actions are morally obligatory. This pious uncoupling of moral concern from the reality of human and animal suffering has caused tremendous harm. (p.66 hardcover)
Harris also argues that when “people riot[ed], burn[ed] embassies, and [sought] to kill innocent people” in response to the Danish Mohammed cartoons, they were demonstrating a “terrifying inversion of priorities” in which the strictures of a particular religious doctrine were held to be of greater importance than the personal security (and expression rights) of other people.
While I don’t necessarily agree with Harris completely, I think he is right about one critical thing: it is important to be able to criticize religion on logical grounds. ‘Because my religious beliefs require me to do so’ is not an adeqaute explanation for human behaviour, and we should not let people justify themselves on such an unsatisfying basis. I think it is perfectly fair to point out when a religious belief seems to cause harmful consequences, or when different elements of the same religious doctrine seem to be contradictory. That isn’t to say all religiously motivated actions are harmful or problematic – just that the fact that they are religiously motivated does not set them in a special category where their consequences cannot be rationally contemplated.