Now that I think about it, Homura seems like a good argument for why antis wouldn't recognize real-life abuse. Madoka is the most important person in her world. She will never stop trying to make Madoka happy, no matter what it costs her, those around her, or as we see in the movie, Madoka herself. Shippers of all stripes often equate "pure" with "selfless," so a shipper who insists on purity could easily frame this degree of obsession as touching. But in real life, "I care about you more than anyone else" could easily turn into "if you leave me, you will never find anyone who loves you as much as I do," or for that matter, "I only hurt you because I love you so much."