I think that’s a feature rather than a bug? It would be unwieldy to make people check every Lemmy instance for duplicate communities, but I’ll be interested to see how that works out over time since (as you noted) we can look at and join communities outside our home instances
Suspension of privileges (e.g., social or outdoor time) will always be a big one as will the threat of solitary confinement. Beyond officially sanctioned repercussions like those though, inmates could reasonably fear targeted harassment or violence from guards if they are “uncooperative” or “troublemakers”