Right. Why should I have to designate a party affiliation to vote in the primaries in Idaho?
This is Idaho law.
Primary Elections in Idaho
So in primary elections, unless the party chooses to allow others outside the party to participate in its primary election, only registered voters of a political party may vote to select their party’s nominees. In other words, at primary elections, registered Republicans may vote only for Republican candidates, and registered Democrats may vote only for Democratic candidates. Persons who are registered as “unaffiliated†(meaning not affiliated with any political party) may not vote for partisan candidates in primary elections unless the party decides to allow them. However, an unaffiliated voter may affiliate with a party up to or on Election Day and vote in that party's election. Independent candidates appear on the ballot only at the general election.