To anyone out there who may be frustrated with how the two major political parties run their nominating processes, please remember the following:
1. Nothing in the federal or state constitutions dictates how political parties are managed. The parties are entirely free to conduct their internal affairs as they see fit. You have every right to complain if you think those affairs are managed poorly or their processes do not reflect the will of "the people", but they are under no obligation to listen to you.
2. The reason party "insiders" can control the nominating process is because they have been there for years and have accumulated the expertise and influence to either work the existing party system to their advantage or change the system to such a degree that their interests have a greater say in what goes on.
3. Systems do not change overnight, so if you are just beginning to realize 1 and 2, you have a couple of options: a) get involved in a party and put in the time and effort necessary to become an insider; b) start your own party from scratch, where you can have an immediate influence on how it is structured and what positions it campaigns on.
4. If you choose b), realize that the way our current electoral system is set up is a huge factor in why things currently are the way they are. The dominance of the two major parties is a result of how we conduct our elections. In our history "third" parties have either i) been flash-in-the-pan movements (often coalescing around a single charismatic personality) that quickly petered out, or else ii) gained such momentum that they ended up displacing one of the existing major parties. That process may take a decade or two, but then you just have two major parties again. If you choose to start a "third" party without also working to change the rules that define our electoral system (primarily single-member districts and plurality voting) the odds are overwhelming that your party will end up in category i). (How many of you remember Ross Perot?)
5. Changing those rules is a daunting, but not impossible task, and much of the work to accomplish it will need to be done at the state level. Pulling the lever for Sanders on one side or Trump on the other will not be sufficient. Neither are "insiders" and neither will be able to wield much influence over the other levels and branches of government that will need to be on board to implement their agendas. You can piss and moan all you want about this on social media, but that will not change the facts on the ground.
6. Regardless of whether you choose a) or b) above, know that it will likely take at least 20 years for your work to produce any tangible results, but either is preferable to c) staying uninvolved and uninterested in the matters that will determine what sort of life is possible for you and for future generations.