My money is on this. You wouldn't typically argue with a kid, but on the internet you probably are.
If you're out and about and a person comes up to you and shouts about how the world is controlled by goats in cow suits, your brain will quickly assess the trustworthiness of this person. Is the person wearing clothes? Is the person rambling/coherent/visibly intoxicated? Are the person's eyes shifting around/manic looking? Does the person smell weird? (I am making up random examples, but I am sure there are many things that every person will look at to gauge trustworthiness).
Most of the above goes out of the window on the internet. Even the shouting part does not usually manifest itself into a website comment (ALL CAPS is less offensive than someone actually shouting in your ear/many people don't know the connotation).
You have to coach them into being more critical of what they read online.
It is easy to fall into misunderstood or outdated ideas. Sharing those ideas with others prompts them to correct any errors in thought as a service to you. In turn, they will receive similar corrections for their misunderstood and outdated ideas as they share them. Collectively, this improves the shared understanding of everyone. The foundation of education.
Spelling and grammar corrections come part and parcel in that. They are given because they equally want to be received. There is really no greater feeling than being able to learn something new, and realizing that you were spelling something wrong, to be able to spell it correctly in the future, fulfills that as much as realizing your understanding of some complex subject was off.
On that note, those of us involved in the software industry know that software testing is greatly benefitted from testing invalid inputs as much as valid inputs. When challenging your ideas, it can be equally useful to try and take an alternative perspective – invalid input, if you will – and see what kind of correction data is returned. If the correction data is poor, what was seemingly incorrect input may be closer to being correct than you originally thought. This can be just as useful in correcting your understanding as simply posting what you hold as being true.
The old adage about asking "How do I do X in Linux?" will yield no response, but stating that "Linux sucks! It cannot do X." will solve your problem nicely captures what online message boards serve. To try and apply a human element to who sits behind the "Linux sucks" statement misses the point.
I used to post online when I was 12. I wanted to be part of the conversation and feel like an adult. What usually happened is that people would label me a "troll" and tell others to ignore me. I would genuinely use the phrase "I'm just asking questions", and people would treat me like I was intentionally trying to inflame the situation.
1: https://nymag.com/intelligencer/2020/09/qanon-republican-par...
I think you'd be able to spot a 9-year-old attempting to engage in "discourse on the internet."
However, I think it's common to engage with people who are in their late teens to early 20s, who are at the point in their lives where their intellectual self-confidence has increased far beyond where their actual understanding is, but they've yet to realize that. They're fluent enough with adult language that they're hard to spot, but they've basically only absorbed one or two big ideas which they mistake for the gospel truth of everything.