This is basic media literacy of the type taught to school children. Without a source, we don’t know whether anyone is even talking about the same thing or evaluate how trustworthy it is. People write lots of things on the internet and since search engines customize results there’s no guarantee that anyone will get the same result.

This matters because someone who is confident that they’re honestly representing the facts rarely needs to be evasive. When you see so many people commenting about something which they assert is true but won’t even name, it’s usually an in-group shibboleth which they are not confident will stand up to scrutiny.