That is a good point made. The report button sort of plays the same role as police presence in high crime neighborhoods. However, self-policing is highly problematic at least in a 1x1 sense. With the other areas there is enough traffic with enough people that most may consider reporting problematic posts. Or you may end up with the group think concept similar to what happens with crimes that happen on the streets near large crowds. "Why should I report it, someone else will take care of it." It is the same reason if you are being attacked and call out for help to single out an individual somehow like, "hey you in the red shirt." So that is somewhat problematic. 

However, I'm not sure how the traffic is within a 1x1. Quite frankly, over the years I have never actually viewed a 1x1 that I wasn't personally involved with. I found no prudence to do so. But I may be the outlier. I'm not quite sure what appeal 1x1 would have with regards to other players with the exceptions of friends and that sort of bias would detract from what might actually be considered reportable material. A friend may give the wrong-doer a little benefit of the doubt with the material in question. And as you already mentioned, if the participants are consensual they may not report the other player at all. 

So perhaps I am overanalyzing things as I have been known to do. But people were provided the option to self-police previously. There was a report button if I remember correctly. And if I am correct in remembering, it failed.