I don't think everyone who believes in some form of the creation myth -- any creation myth -- has necessarily rejected science. I can see where it might seem impossible to have it both ways, but I think part of being religious is accepting that there are mysteries in the world that can't be explained, and having faith. Most religions, not just Christianity, require a certain degree of faith. I think there are plenty of people out there who think that evolutuion and creation are not mutually exclusive.
People having their own beliefs, even if I might think those beliefs are off the wall, doesn't bother me. It is when those beliefs interfere with politics that I think many of us, religious and non-religious alike, get nervous. Of course, just based on my knowledge of US politics, I can say with some certainty that I'm probably not going to have a lot in common with the 6000 year old earth folk, and I wouldn't likely vote for one, but that isn't really because of that particular religious belief, it is because we are likely to disagree on policy issues like healthcare or education or foreign policy.
I think this is important because LE, even though we may see ourselves as non-believers being "right" and on the side of science and logic, there are a whole lot of people in the world, and not just extremists, who think not believing in god is sad at best, evil at worst. I would rather those people not take my lack of belief as evidence that I'm crazy without looking at the whole package, so I suppose I should do the same with others. I think the idea of a creation myth is crazy, that's why I don't believe it, but (all flippant remarks about wingnuts aside) it is a bit unfair to paint the believers themselves as crazy because of their religious belief.
And I think the difference between creation and "flat earth" or any other examples is that the belief in a flat earth is not required by any religion for salvation. There's no "reason" to have faith in a flat earth. Likewise, does anyone gain anything by denying the holocaust? But asking people to reject religion, even if science says they should, is asking them to give up something that is a part of their culture, their family, their community, and very often, is a belief system that gives their lives order and purpose. A reluctance to reject all of that outright doesn't seem crazy at all to me.