The parties organized themselves outside of government as a way to control government to profit themselves. We were never a Democracy, and to the extent the parties have subverted the election process, we are that much less a Republic.
I have never been interested in living in a “dictatorship of the proletariat” no more fond of one dictator a thousand miles away than I am of a thousand dictators a mile a way. Democracy is and should be limited to the vote, the selection process of our representatives.
The parties should only endorse candidates that embody what they see as their core principles. They should only embrace candidates that further the cause of the party. That is their purpose. The problem arises when the only candidates which can appear on the ballot are the candidates from the two parties. When the only candidate which can win belongs to one of the two parties.
This is the situation we find ourselves in now.
I don’t think the GOP should nominate Trump. The fact that he has won primaries has no bearing on his benefit to the party itself. His status as an outsider is detrimental to the party if they embrace him as a nominee, giving him power to set the course of the party for several years to come.
So too the Democrats should not embrace Bernie Sanders if they are not convinced that he would improve the prospects of the party. That doesn’t mean that he shouldn’t be on the ballot. That Trump shouldn’t be on the ballot. It means that the system as it currently exists is broken in ways that most people are only now beginning to understand. What is needed is to break loose from the calcium deposits that have formed around the structures of our government, and shake up the ways that our representatives are selected.

If you are dissatisfied that your candidate will not appear on the ballot, I say “it’s about time. Now roll up your sleeves and get to work” because it’s going to take a lot more than one election to fix this mess.