I don't say intelligent people cannot be happy. But the consensus of opinions on this forum is there is no God. Therefore most people here have to face a universe without a meaning or purpose.
Careful with all that straw. It's a fire hazard.
The idea that a sense of meaning and purpose can only come from a belief in a god or gods is entirely false. In fact, I think it far nobler to choose as one's meaning the understanding (to the best of our abilities) of the structure of the universe as it really is, and as one's purpose the betterment of ourselves and those around us. I don't need a magical agency to validate my wonder at the imaging of a supermassive black hole 54,000,000 light years away, or my joy at seeing the excitement on my little daughter's face as she watches a hummingbird moth feeding from the flowers in my wife's garden. And I don't need an anthropomorphic omnipotence to feel deep love for my family and friends, and to want the world to be a pleasanter place for my species as a whole.
There is no less meaning or purpose in life without gods. In fact, I would argue the opposite: there is a myriad of meaning and purpose without the imposition of the official
Meaning and Purpose™ of some religious dogma, as we are able to find our own. Which is only appropriate seeing as meaning and purpose only exist in our minds anyway, much like love and wonder.
But religious people have belief in immortality of the soul and feel comforted by that.
This assumes that the idea of extinction is universally terrifying, and that no one can possibly experience happiness unless they feel assured that they will continue to consciously exist eternally. Mark Twain noted that he'd been dead for billions of years prior to his birth and it hadn't caused him the least bit of bother. So why should he fear the same nonexistence after his life?
You can't experience nonexistence. And if someone can't find any joy in living a temporally bounded conscious existence, to the point that he/she needs to believe on faith it is boundless in order to enjoy it - if that person can't take joy and meaning from being a temporary part of a great chain of life that extends far beyond any one of us - well then I feel sorry for that person.
It may be that much of their religions doctrines are false beliefs. But that may be because the human mind cannot get a handle on the divine mind. The divine mind is presumably infinitely great, whereas the human mind is limited and finite. Possibly by the fact we are using a physical brain to think with. Occult theory states that when we die the spirit mind expands into greater consciousness because we are no longer held back by the limitations of the physical brain.
It may also simply be a way for our brains to comfort themselves by anthropomorphizing the universe into a form that we think we can anticipate and manipulate. After all, if it is something like us, we can potentially please it and cause it to give us what we want. It may even protect us selectively from what we fear. This, I believe, is the ultimate origin of the construction of all such spiritual agencies.