My partner was keen and I was ambivalent, but without an especially strong feeling either way. There are obviously benefits in both courses through life. So I went with her on it and I have no regrets. It's a very magical experience that our bodies and brains are specialised to handle. Thinking about the changes and reactions I notice in my wife and myself are intriguing.
I had no nagging from anyone and we were together for 8-9 years before having our first. We both have very supportive, model parents. I imagine that new parents with great parents of their own are keen to continue that legacy. I wonder if some with less-ideal parents couldn't see their chance as an opportunity to do better than their own experience?
I think any short term costs (time, money, opportunities) are won back in all the treasured experiences, and then everything from there with independent children is like interest being repaid (IT support in 2050, moving my furniture to the retirement facility, booking cruises, etc). ;)