I don't know who "everyone" is, but their advice couln't be any further from the truth. African cichlids, whether Malawian, Tangnyikan, Victorian, or any of the other Rift Lakes, can be some of the most territorial and aggressive fish in the hobby.
When cichlidphiles say that a cichlid is not aggressive, they are speaking in terms of relatively. They are meaning, they are not aggressive in cichlid terms, which could mean anything from mildly aggressive to semi aggressive. Usually they mean that they will not usually kill all other fish in the tank.