Ok, I went back and read your edit:

EDIT: We DO need to make good rational plans on how to do this, but that planning can be done by a small group of rationalists. I mean only that the front end should be targeted at less-rational people.

Before that, it really did seem like you were using "Shut up and do the impossible" to dismiss MrHen's questions as complaints about the difficulty.

I see now that you meant to refer to the task of figuring out how to do execute the idea effectively. A major reason this was confusing is that no one was complaining that this is hard, let alone impossible. There was no reason to support it with "Shut up and do the impossible". To communicate more effectively, forget the colorful slogans and metaphors (it also wasn't clear that you meant the "save the world" button as a metaphor for the Facebook group, and not just an example), and just clearly state your position, in this case, what you want to do.