There could be a legal argument made that Backpage induces trafficking on its website by not requiring verification for adult services, and is therefore involved in the creation of its content and thus not protected under Section 230. Section 230 could also be amended specifically for adult content to require verification and restrict anonymous payment methods. But the EFF is absolutely correct that in its current form, this would be terrible for anyone hosting content on the Internet because this amendment could be broadly applied to illegal content posted on any content providers website, and creates an incentive to have no filtering of content.
One recent development is this Washington Post article that uncovered evidence that Backpage has actually been actively promoting sex trafficking posts to its site [1]. This would make Backpage unequivocally the publisher of its content, and therefore criminally liable. So it is entirely possible that this amendment will not be needed to bring down the human filth that operate on backpage, but some legal remedy is certainly needed to combat the many existing and future websites that will enable sex trafficking.
1. https://www.washingtonpost.com/local/public-safety/backpage-...