It boggles the mind just how interwoven these major party's that are so-called private are intertwined with the subsequent election of a federal, government, presidential position. Is there justification for anger when there is unfairness within a party? Perhaps, but if it's truly a private party, then I have little reason to allow such private issues of unfairness captivate my attention. If you find unfairness in the electoral process, which is a public issue, then that's a different thing altogether, as it's just as much my business as it is anyone else's in the US. Corruption amidst a private club doesn't move me as it would if it were a public governmental affair.
If you want to run as a qualified candidate on Election Day, then do so with the full backing of a major party or do so without their backing, and if you choose either a major party or smaller party to affiliate yourself with, then limit your anger of unfairness to the private party of your choice. Whether party affiliated or not at all, then fully expect and demand fairness and lack of corruption in the election process that comes after nominee selection.
So what if the Republican delegate rules are not as fair from (oh say) one state to the next. The American people have no grounds to allow that anger to wash over into public domain ... unless the private/public distinction is so blurred from the interwoven aspects of the political process.
It's difficult to even know if I am minimizing my concerns when I consider the fact these organizations are not government regulated, yet when I see constant press coverage, it's hard to imagine that most people even realize that it matters they're private groups, especially when the "R" and "D" next to people's names mean more to some than even the positions they hold on issues.