If Justin agrees with this it would help, in my opinion, make discussions more interesting. If he were to post a comment disagreeing with you he would be arguing so would that make arguing permissible even though he were arguing against arguing? (see “catch 22”)
This does not appear to have any dependency on the quality of ideas. Humanity has a lot of ideas, some good, some not so good, I would prefer that evil people are not encouraged to argue against humanities good ideas. If an idea is not clearly good or bad a discussion debating its merits can be very helpful. That would appear to be an argument so I am not sure if we will see much of that in Discussions.
I am not sure how one should judge items 2 and 3 to see if they are meeting these standards when making or defending their position. I still am not seeing a clear definition of the difference asked in the title question.