I also believe in free enterprise. These sites are private businesses. Their owners have a right to protect their product, so they have rules for use. We all acknowledge that we have read and accept these rules before we are allowed access. It was Republican President Ronald Reagan who did away with the "Fairness Doctrine," in FCC rules. So, we are no longer guaranteed equal access for our ideas and input in media broadcast over public airwaves. One of the arguments in favor of the "Fairness Doctrine," is that media sources can be powerful influencers of how people think. "Fairness" allowed for more than one set of facts to be presented, debated, and judged.
At the same time activist journalism allowed for opinion to have the same weight as facts. I am sure that our democratic republic will survive the loss of an occasional voice of social criticism. However, I don't think we can survive unfettered lying and misrepresentation contained in communications. That appears to be where the companies you cite, draw the line. Their product's value is as a "reliable source." Allowing information they suspect to contain lies to be broadcast on their sites threaten that status, thus their profits.
There are no shortages of venues for insincere, unreliable, and biased presentations of opinion costumed as fact. Fox News comes to mind.