Appreciate the detailed write up. I'm leaving the Oculus product line (I'm not pleased with being forced into anything Facebook) - but was curious what the hubbub was about. As someone that doesn't understand the mass appear of Minecraft, I can see this product would never be for me - FB login required or not.
I have a game development background and can definitely commiserate with the issues you were discussing, too.
Secretly I would love to see Facebook fall flat on their face with this. I doubt it will happen - because they are about to release a headset that is cheap enough to come in a box of cereal - which will be driving tons more children (who aren't legally allowed to be there) into the platform as parents look to keep their locked-in kids happy.
IMHO, this will drive Horizon into a cesspool of half-assed, poorly developed "worlds". Facebook will have to come up with an aggressive "seal of approval" or quality control process - and that will piss people off too. The barrier of entry is so low, it will be like any other community-content driven platform where the tools give just enough rope to hang one's self with (as you have eluded). Abandoned, half-baked projects.
Unfortunately, FB has so much invested in this, they will keep throwing money and resources at it until it can gimp along and be given some stamp-of-success.