It's purely speculative, I haven't heard it anywhere either. The idea might be out there somewhere else, though.

To me, the idea of the "great filter" is like acknowledging that the technical challenges required to achieve type II are so great that a planet needs to maintain global peace (and other components of a healthy environment) for an incredibly long time while attempting colonization. It's certainly possible that something could go wrong after type II status, though. But if the majority are good, they might police the baddies? I dunno. We have no data, except the fact that no one's attacked us yet, or visited in the past (that we know of). It'd just be, ya know, really nice to have interstellar compassion. Imagine reppin' Earth culture at the galaxy-wide disco, and everyone's just chill af.

Like I said to kleinbl00 elsewhere in these comments, it's at least comforting to know that Earth-like planets don't seem to be as rare as we once feared. So I'm sure there are plenty of non-life-bearing planets for the type III guys if they need them for target practice or whatever.