What is your evidence for the claim that gankers are not the primary vocal advocates for Open only, or Incentivize Open threads?
Mostly because a quick survey of such threads shows they aren't. I don't recognize all of their creators, and I wouldn't recognize all gankers, but I do recognize enough of both groups (especially as they were from 2015-2020) to have a representative sample size. Even if I assume the threads authored by those without enough posts for me to know who they are are all gankers, the overlap is probably not enough to make gankers a majority.
Secondly, most of the actual suggestions floated aren't any more conducive to ganking than the status quo. Many of them have irrational prohibitions against ganking. While some gankers may see ganking as a way to pass the time in lieu of other options, I do not believe these are the ones proffering these suggestions either. I'm also fairly well convinced that most gankers do not care one way or the other.
Not saying I've done exhaustive research or carefully applied the scientific method to the question of the demographics of vaguely Open-only advocates...just that the balance of easily accessible information suggests the majority are not what I consider gankers, and do not consider themselves gankers.
I might agree if the claim is that hardcore BGSrs are a vocal set of posters advocating for Open only - but (may be I am wrong about this) - don't many of the BGS influencers murder hobo NPCs to accrue influence? Seems like it would be a double edged sword for them if they were the advocates?
I'm not saying any particular category of player is most vocal in this regard. Indeed, I strongly suspect there is no overarching generalization to be made between those advocating Open only than that they are advocating Open only. Power Players might be an exception, but that itself is a fairly broad category, and not a community I'm very well versed in.
As for the double-edge sword, there is none, besides what's implicit in Open only. Open-only would make a lot of what many Open-only advocates do harder...but that's not a bad thing for them. Someone who thinks the most optimal path to their character goals in the current game is absurd, or a needless grind, is not going to complain about the hardships of changes that bring the game closer to their ideal.