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There are so many different types of sliders and map turtles. They all generally look alike except for tiny ornaments some have or don't have. Because of these minuscule differences, should their differences be considered the same as the differences between human races? or are the differences much greater?

I am not sure you should consider them different races. They are all sliders and some breeds have different characteristics. The red ear is supposed to be more aggressive than the others. Mine is not. The Cumberland is supposed be more calm. Mine is. The yellow belly is supposed to be a little more aggressive and is. My painteds are just little pigs.

The differences are greater than what is among people, we are all part of the same species. The turtles you mention are not of the same genus, though are closely related and in the same family.

RES and YBS are the same species, albeit two different subspecies. But others (graptemys, pseudemys and the like) are not even in the same genus, as steve pointed out already. You should look at their scientic names and check the taxonomic classifications.
Common names are tricky, they rely on appearance or sheer tradition.