Why is it necessary to identify as Shia Muslims instead of simply Muslims? Doesn't the term Shia mean a sect, and if so, doesn't God prohibit the creation of sects in religion?
All Muslims belong to one sect or another, even if they are not aware of it. (Or, sometimes multiple sects) The beliefs and practices they have learned reflect the views of a certain group.
Because Sunnis are the majority, usually "simply Muslim" means "Sunni". (That is, there is no neutral zone.) Of course, within Sunnism there are also varying groups.