Is incest per se evil? I think not. It's just defined as sexual relations between "close relatives". I don't understand why this idea would even possibly be considered objectionable.
In addition, Adam and Eve were the first man and first woman, where we are defining "man" and "woman" as, essentially, Adam and Eve and their progeny. We are all children of Adam and Eve, meaning they show up in everyone's ancestry. But (non-doctrinally, same caveats as Carb gave) that does not mean that Adam and Eve were the first Homo sapiens to walk the earth, or that they were the only Homo sapiens on the planet.
The scriptures make a big deal about So-and-so being a literal descendant of Noah. Whu...? How is that a distinguishing characteristic, if everyone died in the Flood except for Noah and his family? And more to the point: If someone was not a lineal descendant of Noah, who were his ancestors?
I understand that many Saints in the past and even today harbor suspicion and doubt (or outright rejection) of what they consider to be the dangerously false idea of organic evolution. I will just point out that, if we accept a wider interpretation than the so-called literal interpretation of Genesis (which is nothing of the sort), then Adam and Eve and the garden in Eden can be fitted very nicely with the precepts and literality of organic evolution of human beings. Some are threatened by this idea, and that's fine.
The leaders of God's kingdom have not seen fit to instruct everyone to accept organic evolution, or any other scientific theory or model that I can think of, so at this point it's pretty clearly not an overtly spiritual issue. But when we get into weird discussions like "Adam's and Eve's children must have intermarried, brother and sister! Ewwwww!", I think it's time to take a step back and clear our heads.