If not, then we will have some ‘promoting’ big accounts instead of twitter or facebook, we will be back to square one.
100%, yes. If someone posts something illegal and you retweet, you should be on the hook as well.
Another feature: let me bang on the downvote or upvote button multiple times to tell the system how much I like or dislike something. Show me more or less or none at all of that topic/user/etc based on that.
Finally and perhaps most importantly, I'd like to see comments and topics sorted by how much my own personal network of influencers rated them. I don't care that 100,000 idiots liked American Idol. I care how much the 100 people I followed hated it (so don't show it to me, ever).
Some people don't like my idea because they say it will create an echo chamber. To them I say that it more closely models real life. In real life, I generally don't hang around with people who I disagree with all the time. My ideal system would insulate people from me if they disagree with me and me from them. Twitter must have a different goal.
If you only provide a forum, and give moderation power to users (block other users, select what they want), then let whatever speech happens there to happen.
However, if you (as a forum provider, social network, whatever) select the content to be viewed and promoted (either using a proprietary algorithm or human discretion), or you are optimizing for engagement, then you are responsible for moderation failures and suspensions.