@GoldenCookie we seek out what we know and feel comfortable with. Anyone who stays with an abusive partner has been abused. It is the environment they know and the behaviour that they understand. Most people with good boundaries, good self-esteem, who are confident and happy to be assertive without being aggressive will not overlook red flags. Of course it happens every now and then, but generally people in abusive relationships have grown up in abusive households.
I grew up in a middle class abusive household, so I wouldn't have accepted someone calling me a cow or urinating on me, because that was not the kind of abuse I was comfortable with. I sought out relationships with people who were mean, inconsiderate, undermining, soul-sucking, incapable of coping themselves, emotionally unstable and a bit violent etc etc etc.
It is very, very sad and a difficult cycle to break. Personally, I think schools would be better way more time on teaching kids how to buy and cook nutritious food, how to manage their household budget, how to develop good self-esteem, how to be assertive, some basic DIY and then do all the stuff about quadratic equations, prepositions and the Incas of Peru.