Because a religion one can't live is no religion at all, and the true test of a moral code is the likely impact of its widespread acceptance. Is it part of a sustainable way of life?
Religion, circa 2000, has been reduced to being an irrelevant joke, and to preserve that status quo is the most irreligious act possible. We meet on the sabbath, we say a few things that no sane man could believe (but it feels so good to pretend), and then go on and do the things we decide we have to do for the rest of the week, discarding the piously vacuous assertions that we began the week with. Worse still, since we've decided that our real principles are the impossible ones we asserted in church, which we've acknowledged are ones that we can't live up to (read: would make for disastrously foolish policy), we won't even begin to let others persuade us to consider more realistic moral limitations. End result: our religion, in practice, leaves us with fewer guidelines in the pursuit of daily life, not more.
For example ...
On Sunday, a union organizer agrees that if a man should hit him, he shouldn't ever hit back - a distortion of Jesus' message (*) and a great policy, if he wants to get beaten to a pulp. In real life, a bully who meets with no resistance doesn't become gentler, out of a sense of shame, he becomes more violent, out of a loss of fear. But you can't say that in church, because it isn't "nice".
End result: when our organizer is attacked on Tuesday, he grabs a baseball bat, and cracks someone's skull. Instead of saying "try to practice a little restraint, son" (a practical bit of advice, that might have given our man the focus to see that shoving his attacker back would suffice to end the attack, and that he shouldn't be doing more harm than he has to), his priest has told him to not fight at all. So, when he finds that he has to, he finds himself with no moral guidance whatsoever and does his worst.
Our organizer goes home, remembering the preaching that was directed against him earlier, thinking "what does religion have to do with my life, anyway?" On these terms, nothing at all. And that's the problem.
Religion shouldn't be about pretending to believe any number of pretty lies, for one hour a week - and then not only doing nothing to deal with the truth, but undermining the spirit of anyone who tries, seizing on his refusal to live according to the 'officially sanctioned' delusion, as an opportunity to cheaply gain a sense of superiority at his expense. It should be about giving people the right perspective in order, on a moral level, to make the best of the possibilities available for them.
For this to be possible, we need a clear eyed view of reality so we will know what those possibilities are, and to have some insight into what impact our actions will have, ie. what our choices mean. This is yet another reasons we don't have priests here. People have gotten into the habit of expecting priests to tell them what they want to hear, and to convince them that it is true.
Our goal is to open your eyes.
One of those unpleasant realities that we are expected to not believe in, is that prejudice (1) is a basic part of the human condition, regardless of its unfortunate consequences. Given its widespread appearance in children (does anyone really have that much trouble remembering how the child who looked different was treated?) and its appearance in almost every society known to man, it would seem to be instinctual behavior. (Openmindedness is learned, bigotry is innate). In other words, something that is coded into our DNA. It's certainly ingrained in our cultures.
One would expect that that which is innate would be so to varying degrees, and as we've pointed out elsewhere, bad feelings do not go away merely because we pretend that they are not there. If anything, they fester when denied an outlet. Consequently, regardless of whether we feel good about xenophobia, it is a reality that we do have to take account of, and given that it will vary in degree, so will the balance that we would sensibly strike with it, against the good of kindness to the ones excluded.
As we've already pointed out, when kept under control, a degree of localised intolerance can serve to maintain the vitality of a civilisation by preserving its diversity. Consequently, those civilisations that maintain the expression of a small amount of it will tend to expand at the expense of those that don't. Those others will be able to shake themselves out of their relative stagnation, only at the expense of being influenced, and to some extent, tainted, by their less pure spirited neighbors.
Much as there is a sort of natural selection of social orders, as described above, there is, of course, the influence of natural selection on innate psychological traits. Consider a collection of tribes, some of which are devoid of prejudice, others infected with it. The flow of genetic material, will tend to proceed in only one direction: from the more exclusionary peoples to the less exclusionary, because that's the only way immigration can go, especially if we restrict our attention to those immigrants who marry into their new cultures, ie. contribute to their gene pools. End result: natural selection will tend to promote a mild level of antipathy toward those visibly different from one. (2).
Genetic material is not the only thing that an immigrant will bring to his new society. A long noted quirk of human nature, is the difficulty a newcomer will have adjusting to the new realities of his situation, even when what confronts him is what attracted him to his new home, in the first place. For example, the Soviet born American, who shows respect to authority, when it clearly isn't deserved. His desire for freedom may be completely sincere. However, his old experiences distort his perceptions, and new ones take time to form. Thus, given the natural tendency for one to adjust one's attitudes to be more akin to those of the local norm, each immigrant brings a little bit of his old home with him, making his new home a tiny bit more like it.
Again, as with the case of genetic influences, those influences on attitude coming from cultural conditioning will flow from the less open cultures, to the more open ones, without reciprocity. Much as natural selection will thus alter our innate traits, over the ages, until we develop natural characteristics that we might wish we lacked (such as a propensity toward racism), a social analog to natural selection will tend to push those cultures which it helps create, further and further away from attitudes that some of us might consider progressive, in a fairly inescapable fashion. One might add, over a far less than "evolutionary" time scale.
There is, perhaps, a counterbalancing factor - the envy that others in a closed society might feel at the good fortune of those more accepting of those who might help build it. But, if the gates open too much, the resulting flood of those who desire that which the character of the other culture makes possible, but aren't properly conditioned to become part of it, will help to transform their new home, into more of a clone of the one that they imagined they were escaping. That which gave rise to the closure of their old society will serve to remake their new one as well.
So, as with biological evolution, the realities of social evolution will set limits on the attainability of that we may desire (and the reality of what we may hope for) need not be either fair or kind. But if we are to be either, ourselves, we must deal with it on an honest and non-delusional level.
As Stephen Jay Gould points out, natural selection doesn't have a purpose, it just is. Given this, it would be foolish to expect it to serve a higher cause, or to imagine that we, its products, would, in a moral sense, be constructed without defects (ie. conflicts between the various objectives, our fundamental natures make the achievement of, desirable). The word "utopia" is derived from a word meaning "nowhere" for a reason.
Let's continue ...