[quote=@SleepingSilence]
This sounds like you're playing the role of a mind reader.[/quote]
I just calls them like I sees them. It is my [i]subjective opinion[/i] that people who rewrite swathes of other people's works (without being asked to) in, say, friendly [i]creative writing contests[/i] on the internet are people with no awareness of how constructive criticism works in the real world. I stand by my point: they are bad at critique.

As [@bluetommy] has succinctly put it, this is not the same as the editing process with a professional editor, who is there to provide [b]suggestions[/b] on changes that can be made – in a technical sense, and in an overview. The writer can take it or leave it, obviously knowing that if they don't push the edits as far as their editor wants, they may have to hunt around for another publishing company. I don't think any editor would literally rewrite paragraphs in their [i]own style[/i] because that defeats the purpose of publishing an author's own authentic creation.

[b]But even if they did[/b], there's a difference between having someone qualified do it - someone who has an understanding of the craft and knows more than how to do superficial analysis - than some schmuck on the internet doing it, you feel me? That's why it's bad writing advice when it comes specifically from the Internet.

[quote=@SleepingSilence]
(Or when you're writing a fan fiction, because hey guess what, that's rewriting/changing someone's established 'voice/cannon' and making it your own. And that's okay too.)[/quote]
Fanfiction =/= the original work. This is a false dichotomy. I have seen some young writers copy out scripts of movies in their fanfiction, sure, but by and large it's people writing in their own voice, just in someone else's universe. They aren't trying to 'correct' the actual style and cadence of the author, which is something specific to a single person.

[quote=@SleepingSilence]This sentiment could easily boil down to "the author can never be wrong/all writing quality is subjective."[/quote]
This but unironically. All writing is subjective. Like art.

[quote=@SleepingSilence]Because, just perhaps, not everyone that critiques or offers personal advice is thinking "how can I feed my ego today". But does it, in order to help someone get better. (Or at the very least, get them to understand a different perspective.)

And, tell me this...

How can you critique anyone's writing choices whatsoever, when you aren't allow to seek or offer changes?

Because [i][b]all[/b][/i] critique and advice does this. With literally every example you can think of. You are looking, or expecting someone to update something.[/quote]
No one is saying that you cannot [b]suggest[/b] changes. Indeed, I mention in my own post that you can point out technical issues, that you can make comments on plot and structure and anything else you want in a critique. The problem comes from literally rewriting the words an author uses to express themselves and saying it would be better –– because nine times out of ten, the author's authentic voice is a better fit for their own work than a stranger's. 

And even if you [i]could[/i] write it better, it's unforgivably rude to say or imply otherwise, and that's what rewriting does. It also doesn't help a person grow?

Point out the problem, suggest a fix – or better yet, multiple fixes – but don't write the actual fix out in your own words, dude, jesus christ.
 

[quote]So for example, why is "your sentences are complicated and vague" more helpful and acceptable to say, than "Your sentences complicated and vague, so if you don't mind, let me provide you potential solutions as to precisely what I'm talking about." [/quote]
First of all, a crucial difference here in your example from the type of people that I am complaining about: "if you don't mind". If someone has asked beforehand for this specific kind of bad writing advice? Absolutely, that's fine. 

But we both know why this particular example of bad writing advice niggles at you so, and I'd be disingenuous to suggest otherwise. 

Also once more, providing solutions is not the same as rewriting parts of the piece. Any creative writing workshop could tell you that.

[quote=@SleepingSilence]
In both cases, the person giving said advice, is asking the author to change their original work. Likely to make the author's sentences more clear and concise. So assuming both people are doing that in good faith. Where one often gives no examples and provides no solutions. And the other does so. Is the first better because...they put less work into their giving their advice? Is it nicer to leave an author clueless on what the former even wanted? Simply because it there's the chance it will hurt one's feelings a little less, from the sheer lack of context for them to dwell on?[/quote]
My edits to fix up grammar and sentence structure:

"In both cases, the person giving said advice is asking the author to change their original voice. This could be to make the author's sentences more clear and concise, or remove comma splices, or erase unnecessary sentence fragments. So, assuming both people are doing that in good faith – where one often gives no examples and provides no solutions and the other does so – is the first better because they put less work into giving their advice? Is it nicer to leave an author clueless on what the former even wanted, simply because there's the chance it will hurt one's feelings a little less from the sheer lack of context for them to dwell on?"

Unironically, no-one brought hurt feelings into it. People who rewrite bits of text as advice are assholes, yes, but it's not because doing so is hurtful. It's because they generally have no idea what they're talking about in terms of the more 'advanced' techniques of writing – those being nebulous things like style and voice unique to individuals.