This is obviously a really complex and personal decision, but I wanted to focus on this bit:
> If someone is in their 30s, married, but hasn't hit their really time-intensive stretch goals (be it entrepreneurship, financial independence, becoming an industry leader, achieving a senior title, and so on), how should (s)he approach the decision?
Do you really think you'll accomplish your major goals by some point in your 30s? I sure hope I don't - I hope to keep setting and accomplishing (and failing to accomplish) career goals until I retire, if I ever do. And I don't mean necessarily an up-and-to-the-right trajectory, but at least keeping things challenging and fulfilling throughout. I know this isn't what you intended, but it makes it sound like the goal is to get to a certain career "plateau", if you will, and then have kids and rest on those laurels.
I also think it's healthy and a good thing to have your kids see you challenge yourself in your career, to succeed, and yes, to struggle. When they're young, they won't notice, but when they're older, what are you going to say? "Well, son, I worked really hard before you were born so that now I don't have to and we can play catch!" - not a great role model for that child, IMHO.
Even within my local community (far from SV), if I think of some of the most successful tech entrepreneurs, quite a few of them are parents of many children (5 or 6, even!) and had those children long before their businesses became the success they are today.
I don't know if children are as big of a "disadvantage" as we might think. Sure, there are practical limitations, but personally, I found that becoming a parent forced me to become much more focused, prioritized, and productive with the time that I did have available. While the children are young, I certainly cannot be as productive (in total) as I was before, but I have no doubt that once they are older, in school, my productivity will blow away my pre-parental accomplishments due to the increase in efficiency.
As far as risk-taking - this is obviously just an N of 1, but I quit my FT job weeks after our first child was born to go consulting/freelance after a 10-year career as a 9-5er. It's been 3+ years and they've been the most successful and happy I've had. Business is good and I'm also looking into more entrepreneurial opportunities - something I did nothing of when I was single or married without children.