As an example of impacts not necessarily correlated with size, a comms platform for, say, the banking or finance communities, or defence and military systems, would likely have stronger concerns than one discussing the finer points of knitting and tea.
There has not been regulation for online forums for forty years and Earth did not explode or human kind did not end.
Misinformation and disinformation were terms created by censors as an excuse to censor ideas they didn't like, mostly criticism. What we call misinformation and disinformation has been a property of communication since grunting. People are wrong about stuff, even people who we currently think are right. To censor is going back to just knowing the wrong thing for years because someone with censor powers thought they were right.
But how about Trump winning popular vote? Millions of people are sure this is about as bad as explosion of the Earth or ending of the humankind.
Although to be fair to your hypothetical millions, a guy known for repeating getting bankrupt was elected to lead the country. Seems a bit fair to say his track record implies he'd bankrupt the country.
https://projects.fivethirtyeight.com/polls/favorability/dona...
The famed section 230, passed in 1996, is an update to a section of the 1934 Communications Act, which is but one set of laws regulating many aspects of forums. Lawsuits in the early 90s led Congress to modify, but not abolish, the stack of laws regarding all communications technology.
Now that you know but 2 of the many laws affecting online forums, you can dig up plenty more yourself.