Lemeiux doesn't have any particular problem with the caucuses as they are (and I'm not as much saying they're great as I am saying that they should be within the scope of party choice), so we're basically in agreement there. What he objects to is this:
But party nominations are different. They are how parties govern themselves, and the parties should be trusted to know what works best for themselves...It should be up to the parties to decide whether they would prefer a relatively high-turnout delegate selection scheme that would put more influence with mass electorates or a system that empowers smaller, more dedicated groups of party activists. The parties are also best positioned to figure out which influences they prefer (including second-order influences; mass electorates give more power to the media, which parties might not like). More to the point, it’s the parties who have everything at stake here, so they should be the ones to choose.Here's Lemieux:
Given that we have an electoral structure that limits voters to at most two viable choices in most elections, primary and general elections cannot be neatly separated. Barring a greatly accelerated economic recovery, any nominee chosen by the Republican Party has a reasonable chance of being president of the United States. For many House and some Senate elections, the process of candidate selection is the only practically meaningful election given the ideological makeup of some states. Thus, the government has an interest in ensuring some level of fairness in the candidate selection process...On the other hand, Matt Glassman would go the other way entirely: "I’ll even go further: normatively, there should be no relationship between the parties and the state. As far as I’m concerned, the political parties do not, and should not, exist in any public sense."
I'm squarely in the middle on this. In my reading, not only are political parties necessary for democracies, but parties must be both permeable and internally democratic for a polity to be truly democratic. So, contrary to Glassman, I do think there's an important state interest in limiting the extent to which parties are conspiracies of some against the whole.
But "internally democratic" can cover a very wide range of practices, and I'd want to see a very light regulatory hand.
So: if parties design procedures which give activists (and other party actors) more influence and voters-as-just-voters less, that's fine with me as long as those voters can, if they choose, become activists. But I'd have a very big problem with anything that says that some groups can't become active party members, whether explicitly or implicitly, and I'd be okay with the state stepping in to prevent that.