First of all, thank you for coming here to Meta with a polite, calm question as you have done. I know how confusing the rules can be to new users, and it is always appreciated when people ask instead of ranting.
Next, I want to point out that none of the users you mention are moderators. Moderators are elected by the community and have a ♦ after their names. You can see the list of moderators here: https://unix.stackexchange.com/users?tab=moderators
The people you mention are high-rep users. This means they have enough reputation to be able to perform certain actions on the site. For more on the various reputation thresholds, please see https://unix.stackexchange.com/help/privileges.
On to your observations!
Observation 1: New contributors cannot comment on their own posts
New users can comment on their posts. They can't comment on other people's posts (you need 50 rep for that, which is essential to block spammers from commenting). If you really couldn't comment on your post, then that's a bug. Could you please try again and confirm it so we can report it?
Observation 2: A possibly valid edit by a new user is ignored
Your edit can be seen here: https://unix.stackexchange.com/review/suggested-edits/356718. You are removing the "horrendously slow" but you don't actually give any arguments to support it. Also, the message you used to explain the edit was your attempt to contact Muru. So Muru probably thought the whole edit was only to contact him (you need a minimum number of changes to suggest an edit, so he may have thought you just removed the phrase only to get the edit through). If you really feel that "horrendously slow" is worth editing out, you can try submitting a new edit but this time give your reasons for removing it so that the post's author can understand.
Observation 3: Logical reasoning is not required by moderators, only statements
I don't really understand the problem here. First, as I said in the beginning, the user who commented is not a moderator. Second, if a comment has been deleted, why are we still discussing it? Perhaps the author of the comment made a mistake, realized it and then deleted it. In any case, comments are free, you can say what you want in them (you shouldn't, ideally you should only comment about the question, but you're free to write what you like).
In any case, I can see a comment there now:
POSIX read is very limited, so in the context of this question, your read approach doesn’t work :-/. – Stephen Kitt
The comment is explaining that the POSIX implementation of read is limited. Specifically, I assume Stephen meant that POSIX read doesn't support -d or -n, but only -r. This means that your answer won't work with POSIX read. Yes, Stephen could have made that a little bit clearer, but next time just answer the comment and ask for clarifications (always assuming there's no bug that stops you from commenting on your own posts).
In all, I just don't see any problem here nor any reason to think this has something to do with your being a new user. I've been a user for several years now, I'm in the top 10 users by reputation and an elected mod and I still get comments pointing out errors in my answers. This is a good thing!
Observation 4: Plausible solutions by new users are disparaged
This seems to be the same as the point above. As explained, your answer doesn't work for POSIX read since it doesn't support the -n or -d options, and the question was asking specifically about POSIX read. Therefore, your answer doesn't work for the question. Again, this has nothing to do with your being a new user. Also, the only thing that happened is that a helpful user explained what the problem was. I don't understand what made you feel your answer was "disparaged". There's no disparagement here, only a polite comment pointing out a problem.
Observation 5: Self-deletion of a post by a new user is not possible
You can delete your own answer unless it has been accepted. Just click on the "delete" button under the post:
Again, if you couldn't, there's a bug so please try again and let us know. Make sure you are using the same account to log in. Could you perhaps have tried to delete it when not logged in?
Observation 6: Prejudice to moderators and long-standing users
Once again, no mods were involved. And Muru's post doesn't use read -n so it doesn't have the issue that Stephen helpfully pointed out about your answer. Why, then, should that answer have thew same critique? As for who voted, you have no way of knowing that (not even moderators have access to voting data), so I would urge you not to make assumptions.
But no matter who voted, people are free to vote as they like. Nobody has voted on your post (although I would understand it if they had downvoted since one of the solutions you offer doesn't work with POSIX read). Two people have voted on Muru's answer, one person found it good and upvoted and one found it bad and downvoted. So if anything, it is Muru, an established, high-rep user who is facing "prejudice" since it is he who got a downvote. Now I don't think that's prejudice at all, I am just pointing out that he's the only one who got a downvote, not you.
Finally, the SE sites try to be egalitarian. However, because there is the rep system, it is indeed true that sometimes people with more rep are listened to more. This isn't encouraged, and shouldn't be the case, but we're all humans so some people do react differently to high rep users. I'm afraid nobody can do anything about that though since it is down to how each individual reacts. Reputation on this site is supposed to represent the level of trust the community places in a user. Therefore, the more rep you have, the more trusted you are and the more trusted you are the more weight your statements may have for some people. This is just human nature though and is not under any circumstances the official stance of the community or the moderator team.
In theory, every user is supposed to be treated equally. In practice, this sometimes does fail but when it does, if you feel someone is being rude or dismissive of you because you're new, please flag the rudeness or come here and open a discussion on Meta. No system is perfect, and having reputation can indeed breed a feeling of elitism, but we do try and avoid that.