Nearer the top of the atmosphere, the concentration of H2O is much less, and the argument breaks down, because it’s the top layers that radiate to space. Lower in the troposphere, photons are being absorbed and re-radiated, but not escaping.

In general, this stuff is complicated, and it’s easy for people using “motivated reasoning” to come up with the answer they want. Lots of comments reflecting such misinformation appear on HN — it’s frustrating.

So, listening to random people isn’t such a good idea. Much better to read a report from people who study this stuff, like: https://nca2018.globalchange.gov/, which I recommend to technically interested nonspecialists.

(I eat lunch with one of the co-authors of the technical paper in Nature linked to the OP, the press release is: https://www.jpl.nasa.gov/news/news.php?feature=7535, paper is: https://www.nature.com/articles/s41586-019-1720-3)