So lets assign some values to these non provable untruths and truths, and you can tell me if I have misunderstood you.
In this situation and in this forum, we can assume that the non-provable "untruth" to which Khandro refers would be the existence of a supernatural creator entity = a deistic worldview.
The non-provable "truth" in this same situation would be a non-belief in such a being, ie agnosticism, or atheism.
I am not sure I would agree with the inference that is being drawn here. A deistic worldview does not automatically confer a greater happiness quotient upon those who believe; nor does non-belief, or atheism, automatically restrict or limit the joy ,intensity of experience, or happiness in life - There is no evidence that I am aware of that can demonstrate this, and in the absence of any objective evidence, the question surely becomes a strawman hypothesis.
The question appears to me to suggest that, for want of a better analogy,Deism grants technicolour vision in 3D; atheism restricts you to monochrome black and white, 2 dimensional, drab, and dreary.
If, on the other hand, you are saying that if a belief in a god makes a person happy, then we should be accepting of that - I would have no argument with that at all. Feel free, as an individual, to believe or disbelieve in whatever you like if it brings you happiness and peace - and conforms to the golden rule.Feel free to congregate with others of a like mind, if that provides you with comfort, or joy, or structure to your life.
I would only challenge such personally held views when believers use a public forum to contradict the evidence (creationism, intelligent design, man co-existing with dinosaurs, mankind descended from apes) or where those who do believe attempt to change cultural values to conform with their belief ( banning abortion,opposing gender or sexual equality, imposing blasphemy laws, restricting free speech, bending H&S to conform to their religious rites or symbols, assuming a better or greater moral sensibility than non-believers, or believers of other faiths), or those who evangelise about their faith, making statements and claims which are an insult to intelligence or reason.
If you stroll around in public, shouting out at passers-by through your "Megaphone of Truth" that your faith makes you morally superior, or whose way of life is better, or possesses "The Truth " that others do not, then it is not unreasonable to suppose that some people within the world are going to shout back, asking you to justify your assertions, or to challenge statements that are counter to the evidence! :)