The main reason I have always believed the key to having a healthy electorate is to have continuous engagement of all voters and what partisan restricted elections tend to do is break that engagement by many voters.
Over the years potential voters have witnessed the likes of far-left activists making it clear the current political system we have is a sham and that they need to go over it's head to get what they want at the same time you have an increasing number of aggrieved voters in constant denial of reality fanning the flames of ludicrous conspiracy theories given tacit approval and even egged on by far-right politicians and ultimately cheering on the disruption and defiling of our political process with almost all of them proud to have a big fat R on their voter card. Many young people in particularly see this and don't want to have any part of this shit show but the 2020 election was able to get more of them into the fold for the first time and partly because they've seen what's been taken place politically choose to not register with any political party in unprecedented numbers.
Now a primary system open to all will not guarantee more involvement by an increasingly disillusioned voter base but think of the possibilities this could open up. Wouldn't you rather see John Rutherford in a year and a half looking over his shoulder for the threat of a primary opponent making more noise or one making more fucking sense?