Argument: Open primaries often result in two candidates from same party
Adam Summers. "California Open Primary Measure Would Reduce Voter Choice, Violate Freedom of Association." Reason Foundation. June 7, 2010: "under the open primary system the top two vote winners in many districts will be from the same party. According to a Center for Governmental Studies report, more than one-third of districts would likely see two candidates from the same party square off against each other during the general election in this system. This hardly encourages more moderate candidates in such districts, and will give voters that don't belong to that party no real choice or incentive to show up at the polls for the general election. It would also effectively destroy all third parties in the state, as their candidates would rarely, if ever, make the top two. This would make it practically impossible for them to even qualify to field candidates in future elections."
Shawn Steel. "Should state adopt an open primary system?." CA GOP. March 28th, 2010: "The blanket primary narrows, rather than widens, voters' choices. Many of our gerrymandered legislative and congressional districts are dominated by a single party. In these, general elections would be between a Republican and a Republican, or a Democrat and a Democrat. In large, rural districts, there would never be a Democrat on the November ballot. Likewise for Republican candidates in urban areas like Los Angeles and San Francisco. As for third party candidates, they'd effectively be knee-capped."