The best case I can make for religion is, as many arguments on the subject are, in the form of an analogy.
Let us suppose that you and a small party of associates along with several small parties of strangers are hiking in a remote mountainous area, late in the fall, on a poorly marked wilderness trail. In little clumps you are strung out along the trail, and each little clump has been following the clump ahead on the assumption that someone in front knows where he or she is going.
But the clump in front does not have any idea where it is going. At a point where the trail is especially faint the clump in front unknowingly leaves the trail. Before long they begin to see evidence that they are no longer on a trail at all. As they ask themselves whether they have gone wrong, they notice people in little clumps behind them. They reason, if we had gone wrong, why would these people be following us? Someone behind us must know where we are going, and if we left the trail, the people behind us would have stuck to it and would not be following us now.
So they pick their way forward, though the fall evening shadows get long, thinking there must be some kind of shelter, an emergency or relay cabin, just ahead, until in the dimness they confront a sheer rock face where they stop because they cannot go on. The people in the clumps behind them catch up, and they are all gathered at the rock face discussing the fact that none of them, after all, knows where they are or how far back they lost the trail. Too late they realize that they are now all standing on a cantilevered rock which cannot sustain their combined weight, and the whole group falls into a pit..
No one is seriously injured it seems, but no way out of the pit is obvious in the darkness. So the group huddles together, making the best of whatever materials they were carrying with them and awaiting the dawn. In the morning several disturbing things are discovered.
First no one who has brought a cell phone can get any signal with it. No one in the group had left any itinerary with anyone, so it will be days before any of those present are likely to be missed and no one who will notice that they are missing has any idea where to start looking. One person confesses that he opened a gate which had a warning sign on it that the area was closed until spring, and everyone afterwards had no notice so they all have parked their cars in a place out of sight of the main road. There is no reason to expect the area will be visited by anyone before spring, and after the first snowfall, which might begin at any minute, the cars will all be invisible from the air.
A survey of the pit and an inventory of the materials at hand indicates that there is no plausible way to get even one person out of the pit with the materials at hand. There seems to be no source of food and no water, at least not until the snow falls. There are some matches and lighters but not much to burn other than clothing, which cannot be spared. There are a few unpromising plans, such as chipping rocks from the wall of the pit and building stairs of the rocks or carving a staircase out of the walls, or at least sufficient toeholds that a fit person could get out to summon help. The chipping will dull any implement your group may have in no time, so you would have to be using rocks to hammer rocks and so forth. The most athletic among the group have tried forming a human pyramid to investigate the possibility of getting one person over the lip of the pit, but their best efforts have not been close.
Thus you as an individual conclude: nothing the group can do can possibly get even one person out of the pit before everyone starves to death or dies of exposure and the chances of anyone on the outside finding the group in the pit in time to save anyone are vanishingly small.
Now the lie occurs to you: Suppose you suddenly remember that while on the trail, you had been able to get signal with your cell phone, and you had sent a message to someone. Maybe you do not know when that someone would receive that message and when the person getting the message would realize that you have gone missing since, but when both those things happen (if you really had sent the message, which you did not) it would be certain that authorities could find in the phone records which cell tower your phone was using. Surely that would lead, sooner or later, to the discovery of the open gate and the parked cars. That in turn would lead to a large search party, and thus—no guarantees even if you had sent the message—it might be a matter of days or even weeks, but people would be looking in the right area.
If you tell this lie, you think, you should emphasize that it might be weeks before rescuers arrive, by which time many or all of the group would surely die of starvation or exposure if they do nothing. So people must strive to survive as long as possible and try to get out of the pit or at least to get someone out of the pit to bring the rescuers to it, just in case the rescuers are delayed. But in the meantime, the people in the pit will have some hope, they will work harder at whatever implausible plan they have, they will keep examining the pit and trying to think of ways to survive in it and possibly escape from it. And after all, something could happen. They could make a plan succeed. An earthquake or a lightning bolt could open one of the walls of the pit. Someone could discover you by some incredible coincidence.
Now, of course, the overwhelming likelihood is that everyone in the pit will die, whether you tell the lie or not. But they will be hopeful somewhat longer if you lie. And whatever infinitesimal chance there might be of escaping the pit by their own efforts will be ever so slightly increased if they go at their attempts hopefully. And if they can extend their lives in the pit by even a few hours, they will increase the tiny chance of chance discovery or natural phenomena freeing them. Of course the earthquake that might open a wall of the pit might just as well slam the sides of the pit together, crushing the group, and so forth…random events can work both ways.
On balance, you may decide to tell the lie.
And that is the best case I can make for religion.
The lie, of course, is still a lie. All the arguments for the possible benefits of telling the lie cannot make it true.
And to make the best case for religion, of course, one must assume it is the best possible lie with the best possible effects. Good effects, especially in the long term, are not a hallmark characteristic of lies. Pretty obviously there is no prominent real-world candidate for the best-case religion. The real-world lies which seem able to bring hope and comfort have proved just as adept at bringing misery and bloodshed.
This, of course, is the weakness of the analogy. Your intention in telling the lie in the pit is entirely to the good. And so far as I can see its effects are all to the good, even if ultimately it does no good. But the lie in the pit cannot survive the pit. If rescue does not happen, everyone who heard the lie will be dead. If anyone survives the pit, he will learn it was not your non-existent phone message that saved him. You would be happy to have your lie exposed that way. But in the real-world of religion, the lie is perpetuated. It survives the first teller and the first audience. It survives the particular circumstances in which it was told, including the intention and motivation of the first teller. In the long run, the lie exists to perpetuate itself.
I grant it might be possible to devise a best-case lie; I cannot in any event prove that such a lie is somehow impossible. A lie that at the worst does no harm, a lie suitable for all times and circumstances, a lie incorruptible by other lies...the best-case lie at the heart of the best-case religion is a pretty tall order. What truth would be so horrible that the attempt to devise such a lie would seem worth while? That question is, after all, the one unprovable axiom, the only article of faith of atheism: The truth however unpleasant is better than a lie however attractive.