You're actually not liable for those systems failing in the legal sense. As an "interactive service provider", you are protected under section 230 of the Communications Decency Act, even if you are engaged in some moderation of the third-party content you are hosting. It also means that, as the provider, you have the right to "restrict access" to any content you deem objectionable. However, they have to balance this with the fact that they must also ensure that they do not distribute pornographic material to anyone under the age of 18. How they do that, however, isn't prescribed by the law I think, and so it's on a "good faith effort" kind of footing.

No one likes Section 230. Progressives think that it allows for a site to be absolved of the crime of harboring dangerous people (Nazis). Conservatives believe that it allows for a site to harbor people spreading propaganda against traditional values and suppressing "whiteness" or whatever. Following 2016 and Covid, broadly, both political spectrums believe that the provision gives platforms no incentive to crackdown on "misinformation", or to partake in the curation of misinformation unrestricted.

The reality is, Section 230 has been holding the door closed for more aggressive policing of speech and expression online since 1994. Everyone hates it, but no one wants to get rid of it because getting rid of it cuts all parties in the process.

Rhetoric around removing Section 230 is often what drives sites to tighten their controls. Every time it comes up in the media, it is because there is something going on at the federal level. This could be a signal that the feds are going to start this "conversation" up again, but this time through the guise of more explicitly defining what counts as "pornographic" content (to include Trans content of any kind), or to attempt to mandate a federal porn ID system like they do in states across the country. Both of these things might be happening at the same time. I'm pretty sure Reddit doesn't require you to enter state ID information into their site to access it in those states, so somehow they're running just outside the bounds of those ID laws.