What is the motive of a person that......?

when you tell them about other people that have been emotionally abusive to you unprovoked and why it is not good for you to be around those persons and they seem to stay on these peoples' sides? Like, they will say those persons have done nothing wrong but it is 'you' that has turned against you and not anybody else. Surely I would be turning against myself if I stay in the presence of people that are unkind to me? I told them about my sister who always cuts across me in conversation, speaks over my head to other people, ignores me when I open my mouth, but also tells me not to speak over her 1 year old daughters head. My sister is in her thirties. I am 21. She is basically being v. demeaning and a bully by putting me lower than the 1 year old in status and things. She is also a Fundamentalist Christian. I told this person about her behaviour; that it was disrespectful, nasty, narcissistic and undermining and they went on a rant about how 'I have turned against myself'. Nobody has done anything to me..?? That sounds nuts right? They are trying to convince you that you are at fault essentially. Or, you tell them that such a person called you an idiot when you made a mistake and missed a bus. They just said 'idiot' when you called them on the phone in a very harsh tone that offended you..and then instead of saying 'yeah, they should not have spoken to you like that' they say 'yeah well you were an idiot'..They take the other persons side and don't care about my feelings.