I'm feeling silly today, so I'll share my favourite tin-foil hat moment. Consider a political system where only 2 or 3 parties have a reasonable chance to get a significant number of candidates elected (significant means enough to control the direction of policy). Also consider a system where the parties themselves select which candidates that the general voter is allowed to vote for.
So in other words, in any given area there will be 2 or 3 candidates that have a decent chance of winning. Those 2 or 3 candidates are selected by their parties to be allowed to run in that area. Obviously some independents will get elected, but not enough to control government policy.
Now imagine a system where the people who run for their parties are selected by an internal vote inside the party. If you are not a member of the party, you have no say in which candidates are allowed to run in the area that you vote in. Which, of course, seems completely fair because why should outsiders determine which candidates a party runs?
Now imagine that these votes are not one vote per person, but rather vote-by-proxy. In other words, if a member of the party does not wish to vote for candidate selection, they can, instead, assign a proxy to vote for them. In practice, there will be certain very senior people in the party who have a very large number of proxy votes that they can vote with. The average party member will be encourage to assign their proxy to experienced, trusted party leaders because actually attending a convention and voting yourself is a PITA. Through political dealings, there will be big blocks of votes that can can sway the selection very easily.
Now imagine that you are some shadowy entity outside of the political system. You have some money that you want to use to influence the political system. Let's say that you want to ensure that enough people sympathetic to your cause are elected (from whatever party) so that you can control public policy. How much money would it cost?
Let's say there are 3 parties with a realistic chance of controlling public policy. You don't need to bribe every official. Instead you only need to bribe the people with many proxy votes. Those people can insist that in exchange for promoting the candidate to run in an area, the candidate must "tow the party line" on these kinds of issues.
That way the majority of the candidates that realistically stand a chance of affecting public policy are on board with the shadowy entity. The public never really gets a chance to vote on the issue because it has all been controlled at the candidate selection level.
Now imagine that you are a young, idealistic candidate that will refuse to make such a horrible deal just to get selected as a candidate. Well, you won't be selected as a candidate. Every 4 years you will try and try and try and after 4 or 5 times you will realize that there is absolutely no way to be a candidate without playing ball with the party politics. By the time you are 40 or 50, you've become realistic and even if you hate it, you will realize that you must compromise on some issues in order to push through the issues that are more important to you.
And so any "seriously-regarded" candidate is older, because nobody gets to even pay attention to you until you agree to compromise. And even if you agree to compromise, it takes time before the people with the proxy votes trust that you will follow through.
Of course the above is complete fiction. But, I have always thought about it this way: in computer security we feel that if an exploit exists, it is only a matter of time before it is used. The above sounds like a nice little exploit.