sharing a room forces kids to learn to get along. giving them their own room early deprives them from that experience. loud music is not going to work in many places even if you have your own room. if siblings are so incompatible that they can't bear living together than they have bigger problems than sharing a room. physical abuse among siblings points to deeper issues that are not caused by sharing a room, nor does having separate rooms fix those issues.

giving each of our kids their own room reduced our families stress level significantly. it's not 100% necessary, but i really don't think that making kids share a room helps them get along better....