I have been doing genealogy research for years. I have tracked three of my grandparents’ lines back over 600 years. My maternal grandmother’s line has been harder to track, and so far I have only been able to go back about 200 years.
Not a single marriage of siblings or cousins among them, but I did find out that my parents were 12th cousins. They had common (but not direct) ancestors in the 1400s in Sweden and Denmark. My father’s ancestors ended up in Scotland and my mother’s ancestors ended up in Germany.
I have only been doing genealogy research for a couple of years now and have not gone back nearly as far as you have. I did find out, after telling people all of my life that I am not related to those other Kennedys, that my father and JFK were 11th cousins (they were descended from common grandparents in the 1500s). I guess I will need to change my Tagline. No intermarried relatives so far.
I did discover some slaveowners among both my father's and mother's ancestors. My daughter and her husband took DNA tests and according to my son-in-law's DNA test he has some African descendants. So, will my grandchildren have to pay reparations or receive them?
600 years and a few family lines is a drop in the bucket, given that the number of ancestors we each have doubles every generation.
While it is good to know as much you can about your ancestry, if you had the power to go further back to see you ancestors 1,000, 2,000, or more years ago, I dare say we would find plenty of incest, rape, murder, kidnapping, slavery, etc, in the ancestors of every living human on Earth.