False on both accounts.

When two people argue and neither has sources or reasoning, we all suffer.

You're forgetting common knowledge and obviousness.

If I say I'm thinking of getting a dog and someone else on the Internet says credulously "What? What would it ever breathe?" I don't need to find sources to show that dogs can breathe air or that the air where I live is ok for dogs or that dogs don't overly deplete the oxygen meant for me.

That's a bit of an extreme example though. Its fair to assume people will know dogs need to breath air. It isn't fair to assume that people will be aware of economic and political history of Denmark and Finland. The GP comments also don't include enough information, in my opinion, for a person who is interested to easily search for information to fill in the blanks themselves.