Here's a suggestion: "I started this thread with the express purpose of discussing myself/other ENFjs, please do not post off-topic," would probably go over a whole lot better than suggesting that anyone needs your permission to post anything.
There's nothing wrong with posting off-topic, and it doesn't mean anyone is trying to take any kind of power from the wolves of beta-land
You can always request that a thread be split if it starts turning off of the topic you started. Really, when you're in a real-life conversation that happens all the time. The link she posted was in response to the one FDG posted and was meant to make a point.
So, getting back to the topic of ENFjs. It seems contradictory to me to say that you're interested in keeping a mood, everyone happy and cheerful, but then make cutting remarks to anyone "unworthy" which in this thread includes INxjs, anyone non-beta, Joy, and I'm sure there's other examples. So then what's the whole point of acting like you're happy and cheerful and all, when it's really just something you use against people, not for them, and applies only to those that you like? This sounds an awful lot like manipulation to me, and is the opposite of sincerity.