I think a fork should not be a casual decision as the main developer would have put in hundreds or thousands of hours on the project and was motivated to get it to this state. A project by a small team or even a single person will obviously be constrained in many ways.

Now if the project has potential or takes off a 'community' should fork it only if all other avenues have been exhausted and with good reasons.

Its important for a 'community fork' to let the community know the exact rationale or 'community' can easily becomes a excuse for some to seek to control or capitalise on others work. This does not help open source especially if the main developers are too busy developing while those who fork have time to market the fork to a community.