Being able to edit answers isn't even a mod thing. In fact, for most of SO's life, it wasn't even a 'being logged in' thing (you could just edit an answer anonymously). How they wound up with a Q and A site where you could edit another user's answer far more easily than leaving a comment on it I still will never fully understand.
(this kind of thing IMO really added to the utterly arcane set of rules and conventions that makes it feel so inaccessible)
You could not unilaterally edit anonymously; your edit would have been put in a review queue.
It is good that leaving comments is hard. First off, because it was learned repeatedly, the hard way, that removing that barrier leads to ungodly amounts of literal spam. Second because even insightful comments detract from the main intended flow of using the site, which is: you find a question from a search engine, read the question and verify that it reflects what you're trying to figure out, then scroll down to the answers and learn something. The entire point is to not be a discussion forum (which is also why comments were not threaded for most of the the site's life). In fact, the site came into existence specifically because of frustration with what ends up happening on a discussion forum where people can discuss endlessly.
See, what you're saying makes some logical sense in a vacuum but it's so utterly unlike how any other website works that unless you take a huge amount of effort to explain this to people, gently, then it's not at all surprising that people just bounce off of it.
> but it's so utterly unlike how any other website works that unless you take a huge amount of effort to explain this to people, gently, then it's not at all surprising that people just bounce off of it.
It is, and that's fine.
It's incompatible with a site becoming large; and that, too, is fine.
A large site was not required to accomplish any of Atwood or Spolsky's goals aside from perhaps making a profit off of ads. Many other choices were also counterproductive to the goals aside from profit.
Everyone involved would have loved to "explain this to people gently". There was no space provided in which to do it. We had no access to modify the help pages or do anything about user onboarding flows. Downvotes were the tool provided to de-emphasize things and take them out of the way, and to rate quality; so they were used appropriately. (Despite this, and despite public perception, voting was historically very biased in the positive direction.)
Because new questions were open by default, they had to be closed explicitly and in public in order for them to be dealt with. People walked away with the completely incorrect impression that closing a question is inherently a rejection; the explicit purpose and sole effect of closing a question is to prevent answers unless and until it is fixed. It is done with an explicit expectation that fixable questions will get fixed; but the nature of some problems (in particular: missing information) is such that only the OP can do this. There was a period of time in which "closed" was rebranded as "on hold" in the interface, to try to impress upon people that no, they aren't being turned away, they are being asked to take further action. But this was reverted because it was somehow apparently making things even worse.
But also, yes, after telling countless people the same things daily, sometimes humans lose their ability to be gentle. But nobody who's dealt with roughly ever gets to see what the other side had to deal with earlier. The way that people talk about "toxicity" on Stack Overflow comes across like they think it was constantly full of insults and slurs. The evidence shows that the large majority of that sort of content (which explicitly violated the Code of Conduct, and there was a full system in place to deal with this, that pundits often ignore or even lie about) was directed at the curators. One of the most common questions on the meta site is "why aren't people required to explain downvotes?", with the main retort being "why don't you think they should be required to explain upvotes?". But the main answer to that question is because people who stuck out their necks to try to explain the site's standards politely, would frequently get sworn at and even threatened. (I was once openly called sexist for applying these standards, with no evidence beyond the fact that the OP was a woman, which I didn't know at the time).