A group of people working together can accomplish greater things than any one of them working alone. We see it all around us as people rise up against tyranny, or dig each other out from terrible disasters. Cooperation is a force-multiplier.
Which is why top-two primaries (or, as they've erroneously come to be called recently, "open primaries") are a doomed and useless gesture.
First, some vocabulary. If a few years ago you asked anyone what an "open primary" was, invariably they would have told you "A primary election that does not require voters to be affiliated with a political party in order to vote for partisan candidates," [Wikipedia] or something to that effect. But somehow, in the last year or two, the name "open primary" has been applied to what used to be known as a "top-two" or "jungle" primary. In this sort of primary, rather than each parties nominees appearing on separate ballots (and the winner of each party's vote continuing on to the general election), all the candidates of all parties appear on a single ballot, and only the first- and second-place candidates compete in the general election. While all "top-two" primaries are also "open primaries," it is not the case that all "open primaries" are "top-two."
The problem (make that "a problem," but we'll just focus on this one for today) with top-two is, if there are a large number of good candidates from one party (let's call them the "A" party), and relatively fewer good candidates in the other parties, then the A-party candidates could split the A-vote, potentially making it so that none of the A-party members get into the general election, even if one (or more of them) could have defeated candidates from the other parties in the general election. When I wrote about this last May in the lead-up to the vote on California's top-two primary proposal (Proposition 14), I said that "it would be really nice if we could have a party primary before the open primary." I was at least half-joking: such a response is absurd, meant to show that the original proposal is absurd.
Well, the absurdity passed, and now the absurd response has followed. The California GOP plans to hold a party primary in advance of the top-two primary in order to select their favored candidate. [Via Ballot Access News.]
Coordination is a force-multiplier. (So is repetition.) People will always seek to coordinate in order to maximize their effect on a situation. That's why we have political parties. That's why parties want to keep non-members out of the primaries. That the GOP has decided to go this route in California is a simple, logical, and inevitable response to the rules under which they operate.
Proponents of top-two try to claim that it would elect more moderate candidates, and would ease the stranglehold that the two major parties hold on the political system. It hasn't done so in Louisiana, nor in Washington, and it won't do so in California. But there is a change to the rules which we could make that would do those things: spoiler-free, consensus-seeking voting methods, like approval voting or score voting. These would actually change the incentives, for voters and for the parties they organize.