There is nothing from evolutionary point of view more important than having children. It would be highly unusual if nature didn't make that experience overall speaking as one of best things in life.
Speaking for myself, I know that I would hate to have my freedom taken away by having children. I also know that my sister, who has a four year old and a one year old, has been miserable and exhausted for much of the last four years.
I cannot accurately describe the joy that fatherhood brings me.... despite the reduced sleep and increased stress.
By a magnitude of 10x, Fatherhood has surpassed anything i have experienced prior.
If you could choose between a future where your happiness doubled but one of your loved ones died, or the unadjusted future, which would you prefer?
You'd really have to hate your loved ones for that first option to be viable.
Which of these would you choose?
A. Have children and be less happy, more stressed, and have less money and less free time for your a ~25 year stretch somewhere between ages 20 and 60.
B. Don't have children, be less happy, poorer, much busier, and more stressed during those years, but potentially more happy in your old age.
Happiness is a kind of short term thing. Life has better things to offer in my view.
As a not-yet-made-it startup guy it definitely feels like playing on "expert mode". But with a supportive partner and some careful life choices, it feels pretty good. It helps that my cofounder has a kid almost the same age as mine, and we've been going through this together.
Nature plays a big role in it: I really felt like having kids (which surprised me) and I sure will do everything I can to protect them, but my life is a constant fight with depression.
There is probably the opposite mechanism at play: having invested years of pain in them, you value your kids the more time passes.
I'm sure things will improve once they're 4-5 and they're a bit better behaved / we can start sleeping again / we can start having some time for ourselves as well.