I agree you don't have to love just for biological ties, especially if they treat you badly. But, this is just me, I can't imagine not loving my parents, they are my closest family so I do almost love them automatically. Unconditional love, whatever you call it. That's just me personally, I know different people have different relationships. Family ties can be a powerful thing, of course that can be a bad thing. In abusive relationship, sometimes the child can't let go because of their love for their parent. Even when they do manage to break free, they can still continue to love them but the difference is they know it is doing them harm. There are exceptions to this obviously.

My comment on Seth/Sandy was kind of taken from a personal experience, my grandma died several years ago and I was never really close to her but I still cared, even though it didn't have a profound effect on me. In kind of the same way, I think Seth cared. Maybe they could have shown us more but I still think his behaviour was alright. It's true he never really cared much for Caleb but well, Seth was never the most considerate (but he did make self-absorption highly likeble and I love him for it )