Suggesting that US law makes a company legally culpable for all interaction with that company's website has no basis in our legal system. That isn't how our law has ever worked. The first and foremost thing to understand about law is that
intent is as important as the actual act itself.
So, no, there is no way removing the blank check we cut big tech is going to hurt small startups or a community forum. And most of those are going to have human moderators that do a much better job than those "automatic filtering tools" you seem to suggest are a solution.
The whole point here is that automatic filtering doesn't work. We've seen YouTube, Facebook, and Twitter prove that. Of course, Google has hundreds of billions of dollars at it's disposal, but it isn't hiring human moderators, because it has no reason to: Our government holds that Google isn't responsible for anything on it's platform, so it is better off keeping the money as profit.
Now, where it starts to get interesting is perverse incentives: Much of advertising profits comes from malware and scams. Ad companies make billions off this illegal, criminal behavior. And since we've granted them platform immunity, because it's "user content", they're free to keep making that money. They have no reason to take down illegal content, they can't be held responsible for cash cow scams like the fake rehab center fiasco that make them millions. (Source: https://www.theverge.com/2017/9/7/16257412/rehabs-near-me-go...) Even if they get pressured to shut them down, they get to keep all of the profits.
Section 230 protects companies which knowingly (and this is key, intent is important) do not remove illegal and criminal conduct because it is profitable, and they can't be held responsible for it. Section 230 does not protect small businesses, and the marketing to protect it relies on fundamental misconceptions about basic legal responsibility. Companies without intent to profit off criminal conduct are protected by the basic concepts of our legal system: That you can't commit a crime without intent.
It's amazing how the organizations promoting how critical Section 230 is to "small businesses" are funded by the five largest companies in the US by market cap. (The Center for Democracy & Technology spoke out against SESTA-FOSTA in some articles today, Amazon, Apple, Facebook, Google, and Microsoft are all top tier sponsors.)