I think the most interesting (and perhaps hopeful) aspect here is that people now have an expectation of fairness in the selection of party candidates. That's a relatively new phenomenon. In the past, I think people widely assumed that the party was biased towards individual candidates. Even now, that's clearly the case when the sitting President is a candidate. I personally think that expecting an unbiased party structure is unrealistic, given the very nature of the organization. The party doesn't have a product, other than its opinion. The idea that an organization of partisans only arrives at that collective opinion through primaries and caucuses seems quite naive to me.
I don't really understand the outrage. The parties are not part of the government, they aren't held to the same requirements for fairness. The caucuses of the parties are supposed to help them gauge the public perception of their candidates, to help them make a better decision as to which candidate is most likely to win the presidential election. In fact, I expect each party to be biased towards a certain candidate. I expect the party to come together to back the strongest candidate to prevent any possible party fractures. Just look at what happened this time, maybe if the Democrats had gone full-force behind Clinton from the beginning Sanders wouldn't have supporters protesting outside the convention for his very party. Maybe I'm wrong here but I never expected either party to go above and beyond what's required of them and act like they are part of the government.