The person he was responding to was claiming that "literally everyone creating media" is permitted to be used as a source on Wikipedia, which isn't true. There are some issues that are niche enough that the only articles written by 'reliable sources' on them are articles written with ulterior motives. Even if the line between reliable and unreliable is defined in a way we can all agree on, the problem still remains that Wikipedia is only as trustworthy/unbiased as the secondary sources it derives its content from (the claim in the OP).