I don’t have a problem with open primaries, especially considering that party membership has been dwindling over the years (true for both R and D).
I know people like to spin conspiracy theories about Dems crossing over to sabotage the vote, but I imagine the effect of this is statistically insignificant.
It works both ways. I doubt very much that most people will go through the trouble to vote deliberately across the party line. Like you said, statistically insignificant.
This election cycle, it’s very doubtful, since Bernie is competing so well. Motivated supporters would not waste their vote on a R candidate.