Why are my mother and sister the way they are?

Today the three of us went out to lunch. It was pouring down rain and we were leaving the restaurant. I was the last one out the door. There was a feeble old bitty behind me and I just walked out the door and let it shut in front of her. My mother and sister thought this was terrible and I just informed them that I don't do anything for anybody unless I get something in return. My mother and sister acted like I am the most selfish person they've ever known. I don't really care what they think. That's the way I am and I have no plans to change. I think they are stupid for being so nice and polite all the time. My mother later told me that she was so glad I let my sister see that side of me. Because my mother has known about it for a few years now. Why can't my mother and sister see that I'm right to be this way?