"How does that constitute a scientific theory, much less an inarguable fact?"
I'll let the National Academy of Sciences, the most prestigious science institution in the US answer that:
How can evolution be scientific when no one was there to see it happen?
This question reflects a narrow view of how science works. Things in science can be studied even if they cannot be directly observed or experimented on. Archaeologists study past cultures by examining the artifacts those cultures left behind. Geologists can describe past changes in sea level by studying the marks ocean waves left on rocks. Paleontologists study the fossilized remains of organisms that lived long ago.
Something that happened in the past is thus not "off limits" for scientific study. Hypotheses can be made about such phenomena, and these hypotheses can be tested and can lead to solid conclusions. Furthermore, many key aspects of evolution occur in relatively short periods that can be observed directly—such as the evolution in bacteria of resistance to antibiotics.
http://www.nap.edu/readingroom/books/evolution98/evol5.html Arguing that evolution is not science puts you in a very silly position. Since you are basically saying that the scientific community doesn't know what they are doing, and they don't know what constitutes science. Well... until the church starts curing disease and developing new fuels with faith, I'm going to believe what the scientists say...
Archaeologists study past cultures by examining the artifacts those cultures left behind. Geologists can describe past changes in sea level by studying the marks ocean waves left on rocks. Paleontologists study the fossilized remains of organisms that lived long ago. Don't patronize me, especially with respectable examples that are about 1000 intellectual miles from Darwinism.
Are Margaret Meade and Alfred Kinsey are in your pantheon of "scientists" too?