[TangoTrotFox]

I've also had similar thought experiments here. But take it a step further. It's probably safe to say that the current biggest divide in society is in political ideology. Let's just call this left/right, though that's far from precise. Imagine we placed all 'left' individuals in one US, and all 'right' individuals in another completely identical (in terms of physical resources, preexisting infrastructure, etc) US. And migration between these two nations was freely and instantly allowed, but only if you absolutely abided the initial ideological split. How long would it take before these two nations then had their own internal splits with people dividing themselves among some new subissue?

Of course you hit on this with #1, but I think the answer is that there is no limit to the number of partitions. In other words that division is itself inevitable. So rather than trying to ideologically homogenize ourselves, I think it's more important to for people to embrace diversity of views as opposed to attack everything that doesn't conform to, what to them, seems self evident. Because for 'the other side', their views are likely seen as identically self evident. When sides remain incapable of doing anything except working to antagonize the other, in the end the only way things would be resolved is by force of arms which is certainly something almost nobody wants.