Isn't demanding proof or sources for an opinion insulting?

Demanding isn't polite; but if you can't provide a solid basis for your opinion, there's not much reason for other people to find it of value. Often I am wondering if my own opinions are well founded. Understanding the basis for those that differ from mine helps me to challenge my own, and often to modify them.

I'm talking about the effect the tone of conversation on Hubski has on the image of the website as a whole.

I know. What i'm saying is that the tone of the text is mostly in the mental voice of the reader. If one comes in here expecting aggressive speech, that's what they'll get (and considering how discourse often is on the internet, it's not surprising to expect that). However, you could read this comment in a condescending way, or you can read it the way I'm writing it, which is "I disagree with you like an adult, meaning we can use our inside voices and hash our disagreements out".

Isn't demanding proof or sources for an opinion insulting?

No.

You, and everyone in the world, are allowed to hold whatever opinion you choose. However, When you advance that opinion in public - which is what the internet is, regardless of its presumed anonymity - you are opening that opinion to criticism. If it doesn't pass scrutiny, why do you have that opinion? Is that opinion worth having?

You're saying that all views need to be accepted by the community before being discussed?

There are lots of discussions where both sides of an argument will have lots of evidence - Economics, for example, or "How does one run a country?" Disagreement and discussion is great, I'd argue it's most of why we're here. People disagree about shit all the time here.

take this comment tree for example, where I say something dumb, get called on my shit, and I said "whoah, my Bad" then learned a bunch, while retaining that much of my fundamental point was unchanged by what I learned. The world didn't explode - indeed, i enjoyed the whole exchange.

but to an outside viewer, i can see how that comment could look like it includes:

1: A veneer of kindness kept up until a disagreement.

2: A condescending and sarcastic tone.

3: A sense of superiority.

To me, it held none of those things. You're right that tone has an affect on the image of this website, but I say that the tone of this site is not as poor as you perceive it to be, or indeed, as many people who come from other places probably perceive it to be.