"Mark of Gideon" is a Federation episode, explaining what goes wrong horribly after a planet petitions for membership and Kirk visits to check out what it's like. That's all well and good. In some ways, that's all you need to know about Deep Space Nine as a series (the Bajor problem is easy to forget after the long Dominion War years).
Aside from that relevance, "Gideon" is also a lot like a lot of other episodes, in that it's basically Kirk running up against a planet with a particular problem, this one being overpopulation. As usually happens in these cases, the planet has elected for an extreme solution. Happened before, would happen again, across multiple series, usually in one-off episodes.
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Better to remember that it was an effort at exploring not just strange new worlds but those who attempting to join the existing framework. The fact that it's a story template later revisited, and with equally spotty results, is an indication that it's a tough idea that was never truly solved. Even DS9 walked away from it. A challenge to be tackled more directly next time? Although it might be argued that Enterprise did exactly that, as it explored the founding of the Federation. And so perhaps another reason to reconsider that series...
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