When people argue for the existence of something as fundamental in a belief system, such as an objective moral bedrock of reality, they often switch between arguing for its existence and arguing for the importance of believing in it. For example, if one believes that we are presently inside a universe where a deity has mandated objective morality, even in such a case, we still see the “faults” that they claim would emerge without such a reality. It follows that these outcomes happen even if the moral bedrock exists.
What they seem to be arguing for, then, is the importance of believing in it, rather than its existence, since, according to them, it already exists yet the same “faults” still occur. They conflate the two, and what they are really saying appears to be: “The existence of this is not enough; it is important that you believe it as well in order for harmonious interaction to occur.” It is an argument for a belief necessary to achieve harmonious collective functionality. If it already exists, and these outcomes still happen, then it is clearly more important that people believe in it, as opposed to it merely existing independently of belief. Arguing for something's existence is not the same as declaring the functional importance of believing in it.
In other cases, where we know something to be the case and someone does not believe us, we generally warn them about “finding out” that it exists—for example, riptide currents, falls from high heights, or poisonous mushrooms. In the case of moral or metaphysical claims, however, people are warned of the consequences of not believing in it. The argument slides from an ontological claim—X exists—into a pragmatic prescription—believing in X is necessary for desirable outcomes—without clearly separating the two.
Any being that exists does so without my affirmation or recognition. We take this position with everyone around us, and with all those we have never met. I would imagine, then, that a penultimate being would be even more insulated from the qualifier of my recognition and affirmation. I don't think human beings have largely been arguing for the existence of God in the sense that God's existence alone would be enough.
They are arguing for the importance of a shared belief for collective functionality. For example, someone could say, “Yes, I believe in God, but I don't do anything in response to that belief. I manage my own affairs as though there is a higher being uninterested in me.” From there, acknowledging belief in God is then seen as not enough. An interesting formulation might be: “I have so much faith that God exists that I don’t bother with the concept of believing in it or actively acknowledging it.”
When arguing for something's existence as important, one has to wonder, are they worried that if we stopped believing in it, that it would go away, or cease to be? How could it be that disbelief could kill a God? What is being said? >> Belief is the lynchpin, not something's existence. An ultimate being shouldn’t be hostage to belief. If it’s ultimate, it just is. To reduce it to belief is to demote it from being to function.