LOL, how do you think letting anyone run as a candidate without vetting them will turn out?
Absolutely any bad actor will be able to run without intervention. The floodgates would be open. Which is probably what the bad actors calling for open primaries want.
Also, closed primaries don’t add any more vetting. They just mean that the only people who get to vote in the primaries are party members.
This is the definition of vetting. lol
That choice was made by the voters.