I understand the logic behind the legal challenges that political parties have to primary rules allowing independents - and sometimes registered members of other parties - from voting in their primaries. While there really has never been any evidence that outside efforts have led to sabotaging of primary elections, there certainly is evidence that they've led to different candidates getting elected.
The most notable example of this is none other than President Barack Obama. Had he not been able to run up his numbers in open primary states, he would have almost assuredly lost to Hillary Clinton in that bruising primary battle. I'm sure races in open primary states have made it a bit more likely that moderate candidates were elected, although there are probably also some cases where they elected even more ideologically extreme candidates, since some registered independents are affiliated with fringe groups.
I'll let the courts decide if their argument that free association also means that these partisans have the right to not associate with those outside of their party. Other states have ruled differently, but a judge in Idaho ruled against open primaries just this week.
From the Spokane Spokesman-Review:
The judge said expert testimony presented in the case showed that closing the primary “will likely have the ‘very real and immediate effect of … producing more ideologically extreme candidates.’ ” He wrote, “At first blush, that would appear to be a strong argument for maintaining the status quo. But, choosing ideologically extreme candidates is precisely what a political party is entitled to do in asserting its right of association under the First Amendment.”
This isn't the first time that open primaries have been in the courts, or even in Idaho courts. Defenders of open primaries have won such cases in the past, and lost some, so we'll see where cases like this go in the next few years.
What I am absolutely sure about is that it is absolutely unacceptable for the government to pay for any sort of election that isn't open to all legal voters. Any election paid for with government funds should be open.
If the two major parties want to pay for their own primaries, or have caucuses, they can go right ahead and do so. Nobody forces them to externally decide on who they're going to get behind, but just like the government forces schools who take public money to not limit who can go there, the government shouldn't pay for primary elections that aren't open to every legally registered voter.
Government subsidization of partisan political behavior, which closed partisan primaries clearly are... do I have to explain what is inherently wrong with this? But what is new about the two major parties using their power to milk the public of their money for their own ends?
In fact, this seems like a perfect place to start cutting state and local budgets. Wouldn't you agree?