Sorry 1miau, I agree with @hosseinimr93 here: if one posts into a self-mod topic he knows that his post may get removed. This doesn't happen with a "free" topic. Changing this "during the game" is unfair advantage for topic owner.
I've not demanded anywhere to delete old comments from before the topic was changed to self-moderated.
When it's changed to self-moderated, all the comments left before should get treated as it has been before. It's just about any new replies coming after the topic gets changed.
Then, our known message "self-moderated..." topic would be displayed and everyone would see it.
I have added a hint in my OP to avoid confusion.
Just imagine a shady business getting a couple of bad reviews: in your proposal it will be allowed to change to self-mod and remove those. Those users, if they would have known that there's a chance their posts get removed may have been made the complaints in completely different topics.
Once again, I didn't demand that.
Previous comments shouldn't be affected.
This would make sense, but may be more difficult to implement.
I don't know how much more difficult it would be but doesn't sound much more difficult?
So, once a topic is created it can get filled with spam and we can't prevent that, we are just dependent on moderators deleting it?
You can still report all the posts you consider to be spam and moderators will probably delete most of them, if you created that topic.
Sure, it's an option but after all, we would dependent on a moderator to delete it.
It wouldn't be fair to change topics from normal to self-moderated later and I think scammers could abuse that function.
I didn't demand to delete old posts, my request is only for new ones because when a topic is changed to self-moderated, our usual message would show up.
I have added a hint in my OP to avoid confusion.
One option to consider is implementing specific local rules within your OP and enforcing them, rather than creating a self-moderated topic. Any posts that violate these rules can be reported to the moderators for further action.
Yes, it's an option as well but most spammers won't care, unfortunately.
We can't really enforce it, if it's not a self-moderated topic, as it would also require a moderator to delete it.
But it's a good suggestion.
Maybe it would help a little bit after all, which would be already nice.