I'd argue that arguing for a larger population is progressive. The current leader in science, or at least soon to be, is China. It has one of the largest populations too, coincidence? No. The more people that are born, the more "geniuses" that are born and inevitably more progress in science will proceed. From this science we get the things we need to improve lives ie medicines. Another example is India, just look at how many programmers that country is getting, imagine all the benefits that will have for people.
Thanks to liberal "feminists" the native population in Britain is declining (at best small growth or stagnant), the only reason the overall population figures continue to grow is due to new people coming to the country to keep those reproduction numbers growing.
In an article I just read it said that a woman planning to have 3 children (the minimum needed for population growth) should start giving birth at the age of 23\. Most feminists today advocate that women should focus on their career, something that usually lasts till about 30\. By that age a woman is past the age (27) that's ideal to start giving birth at if you want two children.
For the communists of the more liberal persuasion (socially liberal) who think that I'm spewing reactionary nonsense, my position is in line with what the USSR did. After ww2 to 1991 the USSR had a childlessness tax and it was the capitalist wreckers who reduced the tax as time went on [https://en.m.wikipedia.org/wiki/Tax_on_childlessness](https://l.facebook.com/l.php?u=https%3A%2F%2Fen.m.wikipedia.org%2Fwiki%2FTax_on_childlessness&h=ATPjQfms4ssZEOCbo1xuI-xL-hnRept76wRGWbGn-ZMFSfpY92p6Q2wUnbEt67_oNKQG3hODwrfRojrYFwDwxkqYgUiAy2Sam1p3Zow6S9etRUeY4ULofr3hJzXW6Lf9QDzKvTytUvRHebBK&enc=AZOXA9Gr9waW0_Xc7DWatxfBaNnOEcTOslfsxU6WVQbKfpc-YIdi7DQVP4YtLKC9BXiNqRRN33xuu3KAiv-QvIVZllLQuFXbaZ-TkoRblP1C2E_WcGv-dogFzNZ1sFYD2wElM_HyHiWYrJYgQRhxHYpmMhcIxmZK8LK9NzWQJ6jH8kbW6OtyhM802toruc-9hi_6he0n8FAvtYvWiOlbpIS2&s=1)