*I'll* give you the honest answer.Because, in this particular case, you can't make it mandatory.
As a person addicted to meetup.com, I decided to create my own philosophy meetup group last year in Chicago. I had no idea how much interest there would be in the area for philosophy, especially serious, rigorous philosophy, given how most groups found themselves oriented around New Agey stuff. How many people could possibly be interested in philosophy? Stuff like Carnap, Quine, Kripke, etc? Obviously we can't force people to be interested in such an abstruse subject.
To maximize my odds of success, I picked accessible, regionally central locations, with a nice atmosphere and nice food. I defined my target audience broadly, from newbs to students to perhaps even professors, with the priority on getting serious people, but not to the point of forcing myself into an all-or-nothing situation. My main page contained a message that was welcoming, simple, friendly, and accessible.
By keeping the discussions at a high level, the meetup attracted a lot of high level thinkers-- by several months, I was regularly getting 15-20+ people, which I found astonishing. People kept coming back, since I took them seriously, told them hello and goodbye on a personal level, made friends, and did my best to make sure everyone got a chance to interact without sacrificing the content of the discussion.
Another thing I do is centralize power, and keep it as out of view as possible. That way there isn't the perception of power at all, just fun, and if issues do come up, people can talk to me directly instead of blaming the event. A benevolent dictatorship always works better than a democracy. I went to a large sci-fi meetup once infested with INTP nerds, and they made it very ritualistic, democratic, cliquey, with voted officials (ESFJ shadows running amok) and it led to this embarrassing power struggle, with shouting and yelling, in front of like 60 people. The only event I attended there, that's just not the way to run things.
I'm no longer in charge of my old philosophy group, since I've moved on to other personal projects, though group building is an easy thing. Only when we only control what we can control does "if you build it, they will come" becomes an effective working philosophy. No one likes bossy, bullying people.
Here's another honest answer. My brother, an INFP, is not a constant person. I've learned from experience that a "yes" on if he is going to show requires a x3 multiplier-- if he says he'll be someplace in 5 minutes, that means 15. "No" always means 'no', of course, and "maybe" always means "no, because I don't want to get talked into it if I say 'no'."
Lastly, spazzing out when we don't get our way solves nothing. While a lot of women do this, it is no way for a man to project authority. If we want a large crowd to attend our event, and only a few people show up, then getting angry will just alienate the kind people who did make the effort to show up. Why not make the event pleasant for those who arrive? Then they'll definitely come back next time, and may even bring others as well. It also helps to ask others for input and feedback, since if one person has an issue, others likely as well but are just afraid to speak up. So in your workplace example-- maybe people need to be lured out with free food. Perhaps the presentations need to be more exciting. The point is to find out.
A lot of bossy types in my experience tend to be INTJs and ISTJs, who try to hammer the world into preconceived, static molds, instead of going on an adventure and getting organizations to grow organically and dynamically. My ISTJ father always has had problems with customer service departments, because he doesn't have the imagination to see the perspective of the other party, and therefore can't visualize the quickest path to winning through to a solution. Paranoid, he thinks people are deliberately screwing with him, even though it is normal for a lot of companies to have CS issues on 3-4% of their orders, a statistical fact managers take well into account. Getting angry, threatening people, is a way to alienating others and preventing cooperation, rather than securing it. If I have a CS issue, I call up, build rapport with the employee by asking how he is doing while addressing his first name, and then succinctly and directly spell out what I would like done. That way my time on the phone is minimized to about five minutes, instead of a confusing power struggle that lasts for forty-five.