I actually thought of it more as a purely visual combine. So each post still lives in its own instance, and visually you just see them together. Comment threads would live on different instances and the instance mods just mods the community that they own. So it’s a purely Frontend thing.
There’s nothing inherently bad about sugar. It’s just energy. If you intake more energy than you burn it’s getting stored for future use (you get fat). The same goes for almost anything “unhealthy”. Manage your energy intake and almost nothing is unhealthy.