***H: "I consider a belief that adds meaning to life as evidence that one should hold it" N: Define meaning.***
Unfortunately there isn't a universal prescription on the use of this term, and if we get heavily involved in talking about it, then I'll need to be more precise with every use of the term. In this instance, I use the term to be that which provides satisfactory reasons for unfortunate events, or bare minimum it makes the acceptance of those unfortunate facts bearable and somehow provides reason to be hopeful. I concentrate on the unfortunate events versus fortunate and nonchalant events since fortunate and nonchalant events tend not to require explanation - at least by most humans (although this is not universally true).
***H: "Mario, where do you think the notion of truth comes from? I can't see any origination of truth other than what you call aesthetics." N: I think truth is derived from usefulness, which is linked to survival. There is a fundamental difference between aesthetics and usefulness. The first humans to create fire may not have found the process or the result particularly pleasing (perhaps they were afraid of it), but it helped them survive. Thus, the "truth" about fire was arose in order that other humans could survive.***
My complaint with your instrumentalist approach is that it doesn't answer the epistemic challenge of what exactly is provided by a good explanation. When an astrophysicist is asked for the cause of heavy elements emerging from the remnants of a supernova, there is presumably a good explanation coming from astrophysics why this is the case. I think the epistemic complaint is a valid one. Therefore, we need to explain truth not just in terms of pragmatism (e.g., a pragmatic theory of truth), but one that also meets the correspondence and coherent properties of truth.
When I mentioned aesthetics, what I am referring is something similar to Tarski's notion of satisfaction used in his semantic theory of truth. Tarski defined satisfaction as a relation between a sequence of objects on the one hand and a sentence on the other. In his view - very roughly - an object satisfies a sentence if and only if it possesses the property expressed by the predicate of that sentence. In other words, facts of matter are important.
Now, Tarski doesn't go into great detail about how to use satisfaction as a means by which to know if a sentence is true. However, like you said, there is definitely the whole instrumentalist view that a sentence is satisfied if it is useful to us. For example, an astrophysicist finds it useful that we say heavy elements come from supernovas (don't correct me on my layman terminology...). But, that is not the no where near the end of the matter. I believe few astrophysicists would believe that instrumentalism was the end all and be all of their occupation. Rather, there is a tendency in science to think that science proposes the best explanation for things, at least the best explanation within a certain domain of interest to our current observational limitations (i.e., approximate truth). My point is that satisfaction has multiple interpretations when comparing it to the real world. Some of those interpretations are purely pragmatic, some of those interpretations are purely correspondent, and some of those interpretations are purely coherent. Hence, satisfaction is ultimately defined in terms of 'aesthetics' - a relation that humans have with their surroundings which make them believe there is a green light to their interpretation of the world. Green lights can be based on an experience of success with one's actions (e.g., pragmatic), it can be a belief that our perceptions match our theory of what is happening (e.g., correspondence), and it can be a belief that what we are theorizing makes perfect sense of what we already consider true theories (e.g., coherence). Based on this aesthetic appeal, we extend our personal and 'objective' knowledge of the world. This aesthetic appeal might be quite local (e.g., thinking its okay to drive through a green light when we perceive the light as green), or it might be more global (e.g., thinking we are on the right track for a quantum theory of gravity because we have had recent successes in the past few years). The more global the aesthetic appeal, the more exceptions there might be, and hence the more skepticism we might see in accepting that this relation of satisfaction is being met. There are trade offs to be made and accepted.
***There are indeed different types of appeal, and not all of them include aesthetics. For example, it is commonly considered to be 'true' that we will all die one day. I don't find this aesthetically pleasing at all, so clearly there is more to 'truth' than just our desires.***
Since I see satisfaction of truth as an aesthetic relation, I am not referring to something that is fully aesthetic. We might have a whole collection of truths that met our aesthetic threshhold, however we might also have some statements in that same collection of 'truths' that do not appear so aesthetically appealing. We accept those things in order to maintain the collection. What we don't want to do is accept gloomy ideas unless we have to. This is my point with Mario. We don't have to accept agnosticism and we don't have to accept atheism, so why in the heck would we? There's no reason why we should deny ourselves something as pleasing as what theism offers.
***H: "You can choose your beliefs, and as a result those beliefs choose you." N: You're going to have to explain this. It sounds circular to me.***
If you believe you will become an astrophysicist, then you will become an astrophysicist. The belief has chosen you based on you choosing the belief of wanting to be that.
***H: "If we cannot call those meaningful experiences as 'truth' (or 'approximate truth') because we technically do not 'know', then I see no benefit to the concept of what it means to understand something." N: This smacks of the perfectionist fallacy. Simply because we cannot know 'absolute' truth, that doesn't mean we should abandon the concept entirely. A coherent existence would not be possible without some concept of truth. The concept of truth is what makes me think I can type on this keyboard and letters will appear on the screen. If I had no idea what a keyboard was, I would not think this. There is clearly a difference between understanding and not understanding something. The only thing that religion helps me understand is why other people act the way they do. But then I have to ask what religion helps them understand. Eventually, if I follow that chain, I will probably end up going in a circle or hitting a dead end. This is why I am agnostic.***
The point being that truth is based on the relation of satisfaction, and this is based on the aesthetics gained with a certain unjustified belief about our environment. This is faith. It might be faith on a microscale, but it is still a 'leap of faith', and without it, as you say, we couldn't function. Often it is difficult for people who deny this leap as necessary in reasoning that have trouble understanding people who understand the importance of taking these leaps, not just on the microscale but also on the macroscale. However, satisfaction as a concept requires that we think about the whole of what is gained by a particular belief, and often we must be more conservative in our 'leaps of faith' otherwise we would eventually lose the concept of satisfaction by making it too loose to be useful.
***H: "There's no justification to be agnostic when spiritual meaning is a fundamental human need - at least for most folks." N: This is a great line. Perhaps you and I have a different definition of "fundamental".***
I can only go based on my experiences with others, and my experience suggests that most humans need to believe in something more than mere quarks and leptons bouncing around in a metaphysically random fashion. It comes from a need for higher meaning and it is what drives the existence of religion. From what we can tell, religion is quite old for humans, and in my book that is strong evidence that religion satisfies some fundamental human need and always has.
***Simply because the majority acts in a certain way does not mean that the majority represents what is "fundamental" about human beings. Most of the needs of human beings change depending on their circumstances. I would define "fundamental" needs as those which do not (i.e. everybody should have them). This includes food, water, and probably some kind of social interaction. It doesn't go too far beyond that, however.***
I think this is far too limiting. Humans commit suicide, yet I'm sure the far majority of those cases those people had food, water, and some kind of social interaction. For an organism to kill itself it must be acting out of a need. Maybe it is a need that isn't being met, or maybe it is a need to accomplish something with their death (which we are now seeing far too much of recently), but this indicates, at least to me, that there are more needs beyond what you listed.
***H: "Or, more realistically, if someone wants to be dedicated to their religious beliefs, then I see no reason why they cannot continue to believe in hell if that is what they really want to believe." N: If only you could be so tolerant of agnostics.***
I'm not saying that someone is right in believing in hell (or some X belief), what I am saying is that they are acting in their interests and there is nothing always wrong in doing so. What I would stress is that each of us has a responsibility to make ourselves happy. This should be done in guise of seeking truth, but this pursuit doesn't mean that we accept gloomy propositions, at least without a fight requiring the most we can possibly give it. I have to be honest and say that I do see agnostics as white flag waivers prior to the conflict, but that's neither here nor there. If people want to be agnostic, that's fine as long as they do not feel they are somehow constrained in holding this position. This belief was held as a matter of choice (a poor choice in my view), and if that individual is fine with thinking the implications of thinking of their beliefs as true (or one of the implications of their thinking), then that's okay by me (same as the person who believes in hell). However, when asking me what society should believe, then I think waiving the white flag here before the conflict is no way for society to end up.
Warm regards, Harv