If people start doing this they will likely counter-sue and the courts will probably give them a judgement against you for however much their highly paid lawyers cost them. Which could easily be tens of thousands of dollars.
And it might even help them because there are anti-SLAPP laws for this reason.
There isn't software that can detect it to any reasonable degree. Computer vision is still in its infancy. At best using real-world data you will probably miss a huge amount of content. And there will also be a huge number of false-positive, with probably at least several out of a hundred normal images being falsely flagged.
The tech just doesn't work. It's really really difficult to get a computer to be able to tell what's in an image.
Silk Road has nothing to do with anything. Hosts are only responsible for users uploading illegal content if they know about it (e.g. it's reported to them). The Silk Road hosts not only obviously knew about everything happening on the site, but they were actively involved in making money from it. Silk Road has literally nothing to do with section 230.
Do you think Ted Cruz was in on it as well? He posted clips to twitter from the event.