Section 230 protects against all kinds of collateral and contributory liability that a publisher of information might have, not just direct liability for publishing content that is illegal without regard to context.

Weakening 230 means that online services are closer to needing to treat everything that crosses the platform as the kind of legal risk it would be if it were produced and published directly by the company, considering, including in the worst case of conduct that people might allege it contributed to, with the consideration of how attractive the firm is as a deep pockets piñata for lawsuits where the other side has little to lose and much (even if it is unlikely) to gain.

Which is the whole problem 230 was adopted to solve, but conduct by publishers who were found liable even with 230 in place, proving it doesn't need to be weakened to address the conduct has, nevertheless, provided a pretext for an attack on it.