...is that reality is fixed (i.e., that facts do not change) I'd agree it's sound.

If the underpinning is that what we identify as fact is not subject to dispute I disagree.

Your example re: a flat earth is a good example: for centuries the idea that the earth existed as a flat plain was accepted as established fact. Similarly, for centuries the premise that the earth was immobile and the sun orbited the earth was accepted as established fact.

I having been following the political content of this thread--my attention was drawn to the error in your characterization of creationism as being a theory in any way similar to evolution. But I'd posit that in addition to whether something has or has not appropriately been established as fact, although established fact regarding Obama's voting record may be easily verified by examination of the public record, the import of that record is open to debate.