Yeah... He slept with a lot of people (including his half-sister according to one legend) but his father, Uther was way worse.
I have come to the beliefs that historians enjoy unravelling, maybe even fabricating, dirty laundries of old dead people to feel good about their "refined", "educated" present selves. That, or Jacob Geller has infected me since yesterday.
I mean, considering that everything we know about Arthur is made up for the most part, yeah... Historians do do that.