"On the first day, he was a treasure. On the second, he should have been shot." Said of anarchist Michail Bakunin during the 1848 revolution in Paris. At the beginning of an activity, inertia (the status quo) is something to be overcome, but once you are moving in the desired direction, inertia becomes desirable - it keeps you on track. People with the energy and aptitudes needed to get organizations, including companies, started too often are unable to adapt as those organizations mature and become destructive influences. Recognizing their debt to their founders, organizations are often too slow to rein them in, risking becoming permanently derailed.
Rock and a hard place: Having a well-prepared agenda, a strong chair and several assertive people to help the chair keep a focus on the agenda may not enough to rein in the enthusiasts. A level of rudeness may be required, but this risks permanently poisoning the environment for the group and de-legitimizing the leadership.
On the other hand, allowing the enthusiasts to dominate the discussion leaves them in effective control, and all but assures that nothing gets done. People interested in identifying "low hanging fruit" and making incremental improvements quickly become frustrated and drop out.