In my K-12 environment, most teachers want students to reply to teacher created discussion prompts and not to have the ability to create their own discussion topics. It would be nice if, at the account or subaccount level, we could change the default setting for all courses in that account or subaccount to not allow students to create their own discussion prompts. Many teachers do not even realize it is an option for students until a student figures it out, usually with an off topic discussion topic. Then they do not know how to turn it off because to see the checkbox, you have to scroll to the bottom of your settings and click "more options". There are a few teachers who like the ability for students to create their own discussion topics and they could still turn that ability on, but it would be a conscious choice instead of an unconscious one that they have to react to when a problem arises.
I realize not all organizations have this issue or would want this to be turned off. Therefore, I suggest making it a setting at the account or subaccount level to switch the default from "Allow students to create discussion topics" to "Do not allow students to create discussion topics".