Open primaries are a better litmus test of how well a candidate might be expected to do in a general. I’m fine with them.
Not when the other party's candidate is a shoe-in (Hillary). What you end up with is democrats voting in republican primaries to vote for the republican they think will be the easiest for their democrat candidate to beat. Nobody should be fine with that.
You do realize that the ones who won the nomination by winning the open primaries in 2008 and 2012 were McCain and Romney, right? How did that work out for us?