Yeah but you're missing out on what you imagine parenthood is, not the reality of what it is. I'm not saying parenthood can't be great, and most of us are biologically wired to want it, but there's also a far-from-zero chance that it can be heartbreaking. If, for whatever reason, you did not get to be a parent, you can still help children in many other ways and you can still live a life of positive influence in your community and among those close to you, and you will have done far more good with your life than many parents do.
This is all true, but I think I want to be a parent even if it is heartbreaking.
I think of my own parents' experience. My brother is an addict (thankfully sober for a decade now, but it was a long journey). My sister died suddenly and with no warning when she was only 29, and she was 8 months pregnant. My parents' experience, by any account, has been devastating.
But if you ask them whether they would rather never have had my siblings at all? Not a chance. Not even the flicker of a consideration.
I don't think the actually quite high chance that it will be heartbreaking deters me from wanting it. But I also don't consider keeping my heart unbroken a priority. My heart only manages to break when I love, and I'd rather live a life full of both love and heartbreak than forego the former in hopes of avoiding the latter.