All that you say makes sense, but how do you know that "people are fundamentally decent" is a fact rather than illusion?
I say that simply because humanity is still here. I find it unlikely we would have survived as a species without that cooperation. Of course, there is no way of knowing, but we are here, and that certainly is a fact. We have gone through, and continue to go through all manner of terrible things, due to our own stupidity. But 100,000 years ago it was far worse. If humans were solitary and completely selfish creatures, we would have most likely not survived.
But perhaps I should clarify; the phrase... "Fundamentally Decent" is used here as cooperative actions that further the continuation of the species. It is this "decency" that allows us to thrive, or at least, gives us the opportunity to thrive. A person could be an asshole, yet still have this fundamental decency. This has to do with what is best for the continuity of the species itself.
It might not be the way your or your father uses the phrase, but I think you know what I mean here.
It is interesting to see, even though it may have been essential during humanity's beginnings, it seems to break down now. We have amazing technology, and it allows us (forces us?) to be completely solitary. Humanity may need to find a new way for this "fundamental decency" to continue. Otherwise, if we try to use technology to solve a problem that is essentially a problem of the self, the results could be devastating.
All of this technology allows us to be connected instantly all over the world, yet we are the loneliest we have ever been. It is very strange.
If I understand what you are saying here correctly, it is not the individual beliefs so much that need to be questioned (as you say they may come and go), but the root of belief itself - that which grasps for security.
Yes. There are no guarantees, however.
Although these things seem to arise in everyone and it is essentially the same all over the world, you can only see it on your own. Another person can tell you what is there, or how it will unfold, but that doesn't mean anything. Even though they may very well end up being correct, it still means nothing.
These individual beliefs or thoughts are like a grain of sand in the desert. And while all deserts look the same, the underlying process responsible for the formation of the desert seems to be unique. But the process is not unique, as it resides in all of us.
The constructs of this process have the illusion of uniqueness, as they are grown from the experiences and reactions of the self. And everyone says," My experiences are unique," which is true and false at the same time. What happens from moment to moment IS unique, as it can never appear in the same way ever again. But the way the self assimilates these experiences and uses them is NOT unique. It is a solidified and unchanging state, grown from a unique and ever changing moment.
But please do not take my word for it. All of these things lead into one another, and you will see it in your own way, with your own words. It will always be imperfect, but we do the best we can with what we have.