There is a similar debate about making wearing bicycle helmets mandatory. [1] One problem is basically that with cyclists wearing helmets, they and drivers around them might think that smaller safety margins are necessary. (Both physically as drivers drive closer to them and e.g., cyclists more likely to drive at unsafe speeds.)
I think the argument here is the same: the green padlock makes people feel too safe. I could easily buy an argument that if HTTPS was not highlighted prominently as a SAFE thing by the browser, people would pay more attention to other indicators such as the domain when browsing the internet.
But as your parent pointed out we _already know_ that padlocks for HTTPS are the wrong UI here. The goal is to get to the right UI, which you can only do after getting to very high HTTPS usage rates, which we've been working on for several years already.
Tim's toy hypertext system from last century doesn't have confidentiality or integrity at all and the authentication mechanisms are garbage (which is why nobody uses them). So adding these necessary features has been a retro-fit for the past 20 years or so, and unfortunately the original attempt at the retro-fit was done by people who knew nothing about security UX. Which is understandable, this was the era when people thought PGP was usable.
So, we have to get from this cul-de-sac we were in 10+ years ago, to the correct approach, which means some U-turns and all the major browser vendors are more or less on board with that. The padlock will go away (at least from the main UI) as part of the journey, but it hasn't gone away yet because we're not finished. Notice that even going as slowly as we have, every time there's an incremental move Hacker News is full of people screaming about how awful this is, they can't be expected to handle this pace of change...
I think the argument here is the same: the green padlock makes people feel too safe. I could easily buy an argument that if HTTPS was not highlighted prominently as a SAFE thing by the browser, people would pay more attention to other indicators such as the domain when browsing the internet.
[1] https://discerningcyclist.com/2018/05/mandatory-bicycle-helm...