Firstly, let's remember that creationists say they take the bible literally. Well, what about all the evidence in the bible that supports a flat earth? And in the event you did not know -- the flat-earthers are not a novel piece of ancient history. No! They are still active. You can see their website here!
Here are some key excerpts from this great item about flat-earth descriptions in the bible.
The Shape of the Earth
Disregarding the dome, the essential flatness of the earth's surface is required by verses like Daniel 4:10-11. In Daniel, the king “saw a tree of great height at the centre of the earth...reaching with its top to the sky and visible to the earth's farthest bounds.” If the earth were flat, a sufficiently tall tree would be visible to “the earth's farthest bounds,” but this is impossible on a spherical earth. Likewise, in describing the temptation of Jesus by Satan, Matthew 4:8 says, “Once again, the devil took him to a very high mountain, and showed him all the kingdoms of the world [cosmos] in their glory.” Obviously, this would be possible only if the earth were flat. The same is true of Revelation 1:7: “Behold, he is coming with the clouds! Every eye shall see him...”
Or this tid-bit:
Again, Enoch says, “I went in the direction of the north, to the extreme ends of the earth, and there at the extreme end of the whole world I saw a great and glorious seat. There (also) I saw three open gates of heaven; when it blows cold, hail, frost, snow, dew, and rain, through each one of the (gates) the winds proceed in the northwesterly direction (1 Enoch 34:1-2).” This accords well with Jeremiah 51:16 which says, “he brings up the mist from the ends of the earth, he opens rifts for the rain and brings the wind out of his storehouses.” In subsequent chapters, Enoch journeys “to the extreme ends of the earth” in the west, south, and east. In each place he saw three more “open gates of heaven.”
Here is my point: modern creationists believe that the earth is round. They believe the pictures from space. (They don't believe all visual evidence, though -- such as light-speed, or fossils. With those, they invent convoluted arguments to maintain their world view.)
But why the exception for the flat earth? Why not defend that, too? There are actually people out there doing exactly that!
For example, consider "Tom Bishop," over at the Flat Earth forums. Just check out this post.
Curvature results from the fact that on a flat earth we are looking down at a flat circle. And a circle is always curved in two dimensions. The Antarctic coast and other distant continents of the earth are still tens of thousands of miles away horizontally from the observer at an altitude of 100 miles (edge of space), and thus beyond the resolution of the human eye and merged with the line of the horizon, indiscernible and faded with the thickness of the atmosphere. This is why the view is limited to the immediate vicinity below the observer, and why the land fades into a blueish fog as it recedes.
We can confirm that we are looking down at the circle of the earth by noting that shots from amateur high altitude balloons show an elliptical horizon. If the earth were a globe, curving downwards in three dimensions, all curvature seen in photographs would appear as an arc of a circle. However, curvature does not appear as an arc of a circle. The Earth is elliptical in Russian, Chinese, and amateur space photographs. A striking indication of a Flat Earth.
The only pictures which show the horizon as an arc of a circle are NASA's Apollo shots. The Apollo missions did not occur.
So what's my point? That the creationist will pick-and-choose what kind of science to accept, and what kind of science to "debunk," depending on what is easy. It's pretty easy to get people confused when you talk about things like quantum physics, modern cosmology, or even just the technical details of natural selection. That gives them tons of space for subterfuge.
But they know the vast majority of their potential clients cannot reject the model of the spherical earth. But I submit to you the idea the creationist has no valid claim to dismiss flat-earth notions! And the fact they do dismiss flat-earth nonsense is a testament to their manipulative nature.