I have been presented with the following scenario:
Imagine a healthy, intelligent, priveleged young guy with the entire life ahead of him. Say he becomes deeply depressed for some reason and wants to die. Let's also imagine that he is completely atheistic and believe in no intrinsic values or meaning. He has absolutely no desires, not even to get healthy (as this is often the nature of deep depressions). He's standing on the ledge of a building: why should he not jump and get out of the suffering if that's his only desire. If future and potential desires doesn't count, then why should we try to cure him?
My statement that future desires do not count is a descriptive claim that future desires do not reach back in time and influence present day actions - at least not directly. If you want to talk the person off of the ledge, you need link that action to a current desire or it just will not work.
The link you make may be to a current desire that future desires be fulfilled. We tend to have such desires. We tend to be strongly concerned that our future selves be happy - though this is one desire among many and easily outweighed by other present desires (smoking, drinking, failure to exercise, interests in sports as a spectator and in "reality" television). In fact, his motivation towards suicide may come from an (often irrational - but not always) belief that there can be no future happiness. People extrapolate current pain into the far future and see a future they would prefer to avoid. Still, it is the present desire (or aversion) motivating the action.
This is true, by the way, even if you talk about intrinsic values.
Desirism says that you can motivate an agent to act a particular way by giving a person a desire to do that which has intrinsic value, and a belief that X has intrinsic value. This will motivate an agent to realize X. However, his action is still only motivated by a current desire and channeled by current beliefs. We do not find in this any evidence that intrinsic values (any 'reason for action' other than desires) are real.
Correspondingly, you can send a child to church - where praise, condemnation, and other social tools are heavily used to promote a desire to please God. If you also convince him, "X displeases God" you will give him a motivating reason to avoid doing X. Yet, again, the actual actions are fully explained in terms of current beliefs and current desires. Nothing in this provides any actual evidence for the existence of a god or any type of reasons for action in the real world other than desires.
This account of religious motivation supports the claim that many theists make that, if you take away religious motivation, then some people will do wicked things. To the degree that a person has acquired an aversion to displeasing God and a belief that this "wicked thing" displeases God, then that person has a motivating reason with a weight equal to the strength of the aversion to refrain from doing those wicked things. If you remove this aversion - by convincing this person that nothing displeases God because there is no God to displease - then that person will lose some of his motivation to refrain from "wicked things".
It is true, as many atheists (such as myself) claim, that we could better use our social tools to give people an aversion to doing "wicked things" (rather than the more complicated aversion to displeasing god and a belief that "wicked things" displease god), standard practice for many people still takes the second route. Consequently, when people worry, "If you take away a belief in God, you will take away motivation to do good and refrain from evil" is almost certainly true.
However, this common course of action has many pitfalls. For one thing, it tends to use archaic ideas about what counts as "wicked things" from primitive and substantially uninformed people. It is foolish at best to take the word of prehistoric, superstitious, and all-too-human tribesmen as the unerring truth of an all-knowing and perfectly virtuous diety. Yet, this foolishness is practiced and on a global scale. With it, there are a lot of cases in which people are being convinced to do wicked things by giving them a desire to please God with belief that the ideas of these primitive tribesmen - killing homosexuals, killing whole populations of innocent civilians, denying life-saving medical care to a child - pleases God.
This, in turn, highlights a gross inconsistency in a lot of atheist thinking that runs through a great many atheist discussions - proving that the abandonment of reason is not confined to the religious. Many are all too eager to blame religion as the motivating reason why somebody did something evil. Yet, they deny that religion motivates people to do anything good - they credit good to "other sources" (e.g., our biological nature).
There is absolutely no reason to hold to his asymmetry, other than "tribal" reasons of wanting to look at the world in terms of "us -good/them-bad".
However, there is no sense to the idea that these are not symmetric. If religion can motivate evil, it can motivate good. If religion cannot be a force for good, then it cannot be a force for evil. I hold that the first one is correct.
If a person is given a desire to please God, and a belief that charity pleases God, they can be given additional motivation to be charitable. This is true in the same way that if a person is given a desire to please God, and a belief that blowing up a bus or punishing gays pleases God can be motivated to blow up a bus or punish gays. There is absolutely no sense to claiming that the second type of item happens all the time and the first never happens.
All of this ties to the same point. Whether you like this fact or not, if you want to motivate a current action - such as talking a person off a ledge - you must link that action to current desires. You can talk about future desires, but there had better be a present desire that future desires be fulfilled. You an talk about intrinsic value, but there had better be a desire to do that which is intrinsically good (and this still will not make it true that something is intrinsically good). You can talk about what pleases or displeases god, but there had better be a desire to please god - and it still will not make it true that anything pleases or displeases god.
The same applies to trying to "cure" people of depression. The reasons to do so will need to be found in present desires. Like it or not, nothing else will work.