Presidential primaries in the US have several problems. We do it the way we do it because that's the usual way, not because it works particularly well.
The biggest problem is that the people who vote are usually the most political, which means that winning a primary involves going hard to one edge or another. Instead of electing for consistent productive consensus we nominate for short-term TV sound bytes.
The next is polling. The media plus lack of official information equals tons of guessing, and as the primaries warm up, polling becomes the dominant driver of what happens next. Which would be fine, except the polls are often dramatically incorrect, and polls are not votes.
The media are turning this more and more into a sporting event, and the polls are the play by play, except they're being done in the dark.
A bigger problem is the uneven influence of voting. Some votes are worth a huge amount (New Hampshire!) while others often don't have any impact whatsoever. The voting takes many forms—anonymous, public, sorted by party, crossover, etc.
These two problems lead to the biggest one: Parties often don't nominate their best candidate (where 'best' might mean electable or talented, you pick).
Instead of building a growing cohort of excited, committed voters, more often than not the primary process disconnects those that made the 'wrong' commitment early on.
Consider for a moment a party that chose instead to run its primary on Facebook.
Before you list your objections, some of the features:
Everyone would vote six times over six months. Only the last vote would count in the final results, the first five are sort of a live poll, a straw poll for preference.
The voting wouldn't happen in one day, it would take place over a week, with the results tabulated in real time. So you could see how the tide was moving and choose to either engage your friends to push back, or to join in. True fans would vote early and in public, while the undecided might see what's happening.
Each vote would be for three candidates, in order, from most favorite to 'I can live with this'. This method of voting has been shown to allow consensus candidates to rise to the top, diminishing the voice of the angry few.
Each vote might also include a chance to vote for your favorite candidate of the other party, further increasing options for consensus.
Votes could either be in public or anonymized. The advantage of public voting (like a caucus) is that it gets to a truer sense of democracy, in that choices are more easily talked about. But for the reluctant citizen, the vote could be tallied but not identified with a specific individual in public.
Because the votes aren't anonymous in the database, it would be easy to track changes over time. People who supported X are now moving toward Y. When we're talking about a mass phenomenon like voting, it's these shifts that matter. Cultural shift is how pop music works, and it never fails to create a profitable top 40.
The kind of polling we're used to would become obsolete. Too much good data to worry much about making data up.
On the other hand, actual polling based on data analysis of the detailed Facebook corpus would mean that the public (and their candidates) would have much better insight into what people actually want.
This fits in perfectly with the debate channel.
It seems to me that if one party does this, they end up with a candidate that's less bloodied, more engaged and more connected to the public, putting the other party at a significant disadvantage.
As to the most common objections:
A. This is new. It might not work. Absolutely, agreed. Does what we have now work? It costs more than a billion dollars. It occupies a year of our lives, every four. Do you have a better idea?
For me, this is an okay place to experiment, because the primary is merely the party's chance to figure out how to run a candidate. As a result, it's always been quasi-official and always been a mess.
B. There are all sorts of opportunities for fraud. Yes, absolutely, But almost certainly only on the margins, probably no worse than we have now, particularly when you consider the tiny number of actual voters in the current system.
I'm imagining a public, transparently run app that lives within Facebook. Hard to do, difficult, risky. But probably better than the current alternative.
C. Some people don't have Facebook. Yes, but in four years, far fewer won't have access, and we still have the library. Spend some of the millions and millions of dollars we spend on elections outfitting libraries with more computers instead. Because the voting takes place over a week, no issue with lines, nor hanging chad. It's worth noting that today, in order to be an effective voter, you need a TV and a car, both of which were new technologies a hundred years ago.
Your mileage may vary. Doesn't it always?