Most arguments not to have kids and most arguments to have kids are incredibly flawed and can be toppled incredibly easily. It's just a post hoc rationalization of how you actually feel, and people are uncomfortable with the fact that their most important decisions sometimes aren't that rational, or that they are sometimes environmental and that they could have easily been another way.
There's a minority of people who would never find a way to be happy again if you made them have kids, and a minority of people who would never find a way to be happy again if you made them not have kids. The rest of us could probably swing either way, maybe a little more or less happy on one end than the other, and that's what all the fuss and the discussion is about, because you literally don't know and want to reinforce your decision for yourself.
I can definitely see some of the more basic pros and cons. It's nice to have permanent family members that are very closely connected to you and are way younger than you, someone who literally sees you into the afterlife. It's not to be underestimated because at one point, for some people earlier than others, you start feeling like the world is shrinking and you know less people and all of those unpleasant things about growing older start weighing on you. On the other hand, the daily work of raising kids seems like absolute drudgery, and avoiding drudgery if you can't see the benefit of it is wise. Maybe years of doing wax on, wax off 12hrs a day on top of everything else I do would make me a much better person, but I don't really know that and it's hard to make a connection between point A and point B, so I wouldn't be excited about doing it personally.
So to answer the weird WR question, yes, it's okay for some people not to want to have kids, because even at these replacement rates, enough people want to have kids that there will still be a substantial amount of people left to further humanity until the planet explodes anyway. Everything else is just personal choice, or personal accident, or personal "it seemed a good idea at the time", or personal life plan.
I've got it in my head recently that I want a big family, like 7 kids. Anyone from that situation and know how to make it work?
Not to be rude, I'm just extremely curious where do you get all these big and specific ideas in your head? At first it's considering Catholic, not a lot of people convert into religions they weren't born in , especially "Catholic" specifically as opposed to generally just Christianity or Judaism or whatever. Now it's having seven kids as an abstract thought, as opposed to "I specifically know and have talked to someone who makes it work and I got the impression it would be great for me, plus I already have someone I want seven kids with".
Again, I apologize if it's too personal, but people don't just say "I wanna go to med school to become an ear doctor and live in this one specific village in New Zealand that I have never visited". Has to have an interesting story behind it at the least.