Given that they are not operating as neutral public venues then they should also not be afforded protection under Section 230. If they actively moderate they should be fully liable.
The very point of section 230 was to protect companies even if they did moderate. What you are suggesting is that section 230 should be repealed, and let the courts sort it all out.
IANAL but I've seen enough controversy around this to mention that not everyone agrees with that interpretation of 230 or its ramifications.