AFAIK users didn't actually upload content to the site. They submitted it and then Mr Moore or someone else posted it. I'm also pretty sure he wouldn't honour take down requests.
Is there a large chasm between "upload content" and "submit [content]"?
Is the difference in the latter case just that someone clicks "ok, post this"? I don't think that a quality-review (or lesser, a mechanism to queue and release content to the site slowly over time) turns user-generated-content into site-generated-content.
If Youtube did a quality review, it would still be UGC.
If Youtube did a post-facto quality review (to remove copyrighted music), it would still be UGC.
...
Not honoring takedown requests is a different matter, and just sounds like a dumb call.
Just in general, the difference between having an editorial gatekeeper, and not, is that it gives the site operator actual knowledge of what's being posted. An example of how that would matter is the DMCA safe harbor, 17 U.S.C. 512(c)(1)(A), which requires the service provider not to be aware of facts or circumstances from which infringing activity is apparent.[1] But "how much did you know, when?" is a crucial question basically any time we hold someone responsible for something under the law, so "we knew exactly what was being posted to our site the whole time" is pretty different from "we couldn't possibly keep track of everything that was being posted to our site."
It has done in the past, at least if the person doing the posting added their own editorial comments as I believe Hunter Moore did. However this issue hasn't come up so far because the main lawyer pursuing most of the civil cases, Marc Randazza, strongly believes this shouldn't affect section 230 immunity.
The distinction is very important. The intent of Safe Harbor provisions is not to allow sites to blithely host infringing without possibility of reprisal as long as they take it down when asked. The intent is to relieve sites of the unreasonable burden of both being aware of and policing everything their users do — to allow them to act as sort of a "dumb pipe". If you have personal knowledge of infringing content, you are still expected to take it down even without a DMCA notice — and it is certainly not OK for you to post infringing content yourself.
(Standard IANAL caveats apply of course. I think I have a reasonably good layman's understanding of this stuff since my work touches on this stuff, but you should talk to your lawyer if you want concrete advice.)
I don't think his website would have existed if he had honoured takedown requests. The entire premise was that these pictures are hosted without permission (and according to the Jezebel article about 90% were). If he honoured DMCA requests then that would become widely known pretty quickly. Part of the point of the site was to publicly humiliate the women, so if they had any easy way to get rid of the pictures, it wouldn't have had the same impact.
'Is there a large chasm between "upload content" and "submit [content]"?'
There would have to be the most enormous chasm, because the latter includes every publication that uses the work of freelancers, which is pretty much every newspaper and magazine, and their online equivalents, everywhere.
