It's not nonsense. The website I work for does exactly this, for exactly this reason, and so do many others.
you may of course volunteer to police content in advance, if you have the resources to do that. it's your website, you are free to publish or not publish. but that approach is simply not practical for a large website, like google.com
when I wrote "nonsense", I meant your claim that a website has a "duty" to police third-party content in advance. And I still think that is nonsense (at least under US law, which I was excplicitly referring to), there is no such duty. Other jurisdictions may be different, I don't know. It's ok that the website you work for polices 3rd-party content in advance, but that does not create a legal duty for others to do the same.