I wouldnt say siblings hate each other, more like plain old sibling rivalry, trying to one-up each other, to be the best child in front of your parents, also most siblings live together and well if your around a person for too long you can get really sick of them. Especially if their close in age.
It's natural. We say that we hate each other, but do we mean it? No. Half the words we say to each other, we don't mean at all. My sister and I always argued in the past over the most dumbest things, but in the end, we still loved each other.
Siblings fight like everyone else. No one's prefect nor are we all the same so there will be disagreements especially with the ones with. It part of a healthy relationship to have disagreements. For example, think about spouses. Or a mother & child. So siblings fight sometimes & they get along at other times.