Take that same effort and apply it to other areas of your life, where the happiness research is more clear, and your return on investment will be much higher

The outside view is that parents put way more hours into parenting than non-parents put into any of their meaningful projects. If I have children, I will put in long hours because I will need to. In my current life as a non-parent I work a full-time job and put some effort into side projects, but not that much effort. If you're already using your time efficiently to accomplish cool things, you can expect that parenting will take away much of that time and cause you to accomplish less. But if you're like most of us, you'll just have less time for goofing on the internet, etc. Compared to whatever it is you currently do in your spare time, producing well-reared children might be quite a high-impact thing to do.