I agree this is a little off topic. Unless somebody minds though I'll reply, because I find this topic a lot of fun :) Also there is some purpose to my reply, which I'll finish by mentioning.
This is something of a reiteration but I do feel there IS an ultimate reason for action. It's just that it's bound fair loosely to objective reality and rather more underwhelming than many would like (being again the subjective experience of positive emotion, realized through neurological constructs). I think it's less that the chain has to unravel, and more that people realize it's tied loosely to the terrain and they can move it around ("so if I change what I enjoy, I change what has meaning...?"), which can be rattling. The chain does have an end, but it's not in objective reality and basically amounts to "just because". But what other end to any such reasoning could there be?
I also have a desire for a goal larger than myself, and from personal and observed experience tend to think (mere opinion) that having such a goal is actually the most efficient way to gain the greatest personal happiness. I choose to believe, like most do, that other people have consciousness, and that like me they experience pleasure and pain. While I spoke earlier just of my own personal pleasure, I apply my rubric more broadly to include the pleasure I believe other people experience. With roughly 6.7 billion people on the Earth, bringing as much positive emotion to as many as possible is a goal so large I can hardely grasp it. (I'm intentionally ignoring the finer points of utilitarianism here, just to give the basic idea of where I find meaning.)
I do actually have some purpose for writing this beyond my own amusement. In my experience there are roughly 3 ways to react to this view of meaning, if you accept it. Some like me basically shrug and don't feel it changes much. Some people do become apathetic and effectively depressed. Some people use this as an excuse to only do the things they were going to do anyway, applying the view selectively. As for the second group I find meaning in their happiness and perceive their moroseness to be entirely unecessary, and as for the third group, I find the application irrational (and likely to lead to a net decrease in happiness). Either that or rational and entirely selfish, which from my perspective of seeking the greatest happiness for the most people puts me at odds.
Human beings are all crazy. And if you tap on our brains just a little, we get so crazy that even other humans notice. Anosognosics are one of my favorite examples of this; people with right-hemisphere damage whose left arms become paralyzed, and who deny that their left arms are paralyzed, coming up with excuses whenever they're asked why they can't move their arms.
A truly wonderful form of brain damage - it disables your ability to notice or accept the brain damage. If you're told outright that your arm is paralyzed, you'll deny it. All the marvelous excuse-generating rationalization faculties of the brain will be mobilized to mask the damage from your own sight. As Yvain summarized:
I find it disturbing that the brain has such a simple macro for absolute denial that it can be invoked as a side effect of paralysis. That a single whack on the brain can both disable a left-side motor function, and disable our ability to recognize or accept the disability. Other forms of brain damage also seem to both cause insanity and disallow recognition of that insanity - for example, when people insist that their friends have been replaced by exact duplicates after damage to face-recognizing areas.
And it really makes you wonder...
...what if we all have some form of brain damage in common, so that none of us notice some simple and obvious fact? As blatant, perhaps, as our left arms being paralyzed? Every time this fact intrudes into our universe, we come up with some ridiculous excuse to dismiss it - as ridiculous as "It's my daughter's arm" - only there's no sane doctor watching to pursue the argument any further. (Would we all come up with the same excuse?)
If the "absolute denial macro" is that simple, and invoked that easily...
Now, suppose you built an AI. You wrote the source code yourself, and so far as you can tell by inspecting the AI's thought processes, it has no equivalent of the "absolute denial macro" - there's no point damage that could inflict on it the equivalent of anosognosia. It has redundant differently-architected systems, defending in depth against cognitive errors. If one system makes a mistake, two others will catch it. The AI has no functionality at all for deliberate rationalization, let alone the doublethink and denial-of-denial that characterizes anosognosics or humans thinking about politics. Inspecting the AI's thought processes seems to show that, in accordance with your design, the AI has no intention to deceive you, and an explicit goal of telling you the truth. And in your experience so far, the AI has been, inhumanly, well-calibrated; the AI has assigned 99% certainty on a couple of hundred occasions, and been wrong exactly twice that you know of.
Arguably, you now have far better reason to trust what the AI says to you, than to trust your own thoughts.
And now the AI tells you that it's 99.9% sure - having seen it with its own cameras, and confirmed from a hundred other sources - even though (it thinks) the human brain is built to invoke the absolute denial macro on it - that...
...what?
What's the craziest thing the AI could tell you, such that you would be willing to believe that the AI was the sane one?
(Some of my own answers appear in the comments.)