I dont think people like mewho dont donate money, time, or influence to a given political partyshould have any say in how that party selects its nominees. As the Supreme Court has repeatedly ruled, parties are private organizations whose freedom of association (and exclusion) are guaranteed by the First Amendment. Letting non-members participate in primaries and caucuses prevents the parties from developing any coherent ideology and reduces them to large focus groups.
Voting in general elections is a right guaranteed by the Constitution; helping a party select its nominee is a privilege subject to that partys whims. Quid pro quo, Sunshine.