The thing is that Sam/Ruby is such a beautiful example of a toxic, abusive relationship but it gets ignored because of the "demon blood"
She manipulates him the entire time. She isolates him from his friends and family and makes him dependent on her. Then she reinforces the isolation every time he starts moving away from her by saying all these horrible things to him about how if he lets himself be controlled by someone (Dean) he's weak for doing so and that only by staying with her can he make himself strong and all the while she is undermining him.
If we focused less on the "drug addict" aspect of Sam's S4 storyline and more on the "he was the victim of domestic abuse" I think more people would be sympathetic to that arc.
(That being said, Sam absolutely killed human people in his pursuit of his blood addiction and he should have to take responsibility for those actions even though he was manipulated into starting down that path)