Why do the states run the primaries, anyway?

Marc reports that the Justice Department may have to OK the new primaries in Florida and Michigan:

Here's the reasoning: while a federal judge last year upheld the DNC's right to interpret the rules of its own primary -- even if those rules meant the technical disenfranchisement of an entire state of voters -- the ruling did not touch on the form of the election itself.

When a party decides to change its rules in midstream, five counties in Florida and two counties in Michigan must ask the Department of Justice's Voting Section to make sure that the new rules do not violate the rights of any aggreived minorities. Alternatively, they can ask a federal judge to bless the new rules, but that would take, at the very least, six months.

According to the Obama campaign, voting rights act provisions that govern pre-clearance requirements apply to primaries. So the Florida Democratic Party and the Michigan Democratic Party would be required to submit to the Justice Department their vote-by-mail procedures for close inspection.

What exactly is the logic behind the state controlling the delegate selection process of the political parties? They're not organs of the state--they're supposed to be the voice of the people. It's not clear to my why the states get to do things like set their primary dates in defiance of the party.

This sounds like libertarian quibbling, but I actually think this matters. To be sure, I think we're stuck with the two party system, but I see no reason that the state should help to institutionalize the dominance of these particular two parties. The state's job is to make sure that elections run fairly; the party's job is to nominate candidates. Getting the state involved in the latter, or the parties in the former, only leads to trouble.