The suggestion doesn't prevent non-faction members from helping out. It's a pretty fair and reasonable suggestion because it maintains the fact that dominions--which are strictly for factions; only they can start them--should be a faction effort. So why shouldn't the amount of non-faction members be limited to the amount
of faction members involved?
By using the example Hal linked above; if a thread has 8 faction members and 15 non-faction members then that's about twice as many people not part of the faction doing the effort for a faction activity. The one thread in particular; roughly 38% of the effort was done by the faction that actually started it. 24 posts -- barely 25% of the thread -- has been achieved by the faction involved yet it's over half way done due to non-faction effort.
Don't get me wrong, I'm only using that as an example. I don't even have to go through every once-upon-a-time dominion to know that similar cases do exist. This just happens to be a recent one which I can use as an example.
Faction's should have to put in a majority effort to complete a dominion. They gain the planet after all. It'll make it harder for factions to gain planets, in a sense, but shouldn't that be the case?
Do we want another map that looks like this?