When working on the extremely messy GMO case at Wikipedia, I was accused of being a paid shill by Monsanto. Tons of people were. And I'd bet extemely no good money, nobody was. Recently, similar parallels have emerged with regards to Bernie Sanders. If you aren't supporting Bernie, some will say, you're stupid, misinformed, or paid off. Plenty of people are misinformed, and plenty of people are stupid. But plenty of informed, rational, non-financially motivated people are opposed to Sanders.
It really is pretty telling when the first thing one does in response to criticism is challenge the person making the statement, and not the person making the validity of the statement itself. This argument has been used a lot, but no matter how many times it is used, it doesn't become more valid. Not only are these ad hominem attacks not correct, oftentimes the attack they level at the person making the statement is false as well. It's oftentimes a sign of intelligence to be able to understand or be able to play devil's advocate for the opposition.
Those who say "I just can't understand why anyone would support the opposition" oftentimes have a very poor understanding of their position. Their position may be based upon any number of things. A positive view of socialism, or a feeling they have been wronged. An intellectual identification with democratic socialism. Or even, gasp, self-interest in that they want their student loans repealed. None of these are bad reasons, per se, but then one must think about somebody voting for a Republican. Their social and moral values differ. They may be well off and not want to be taxed. They may be poor off but still harbor the dream of making it big, and see low taxes for the wealthy as part of that. Their fundamental worldview likely differs. For some voters, it isn't so much that they aren't aware of the facts so much that their worldview is different. Do keep in mind that during the Cold War it was pretty out there to be a socialist. It was the next step to communism, and it did tremendous harm to the millions of Soviet residents. That they don't want to move that direction may not be 'progressive' but should everyone be a progressive? I'm not sure I have an answer for that question, but the fact that this line of reasoning raises, rather than eliminates questions is crucial. I would struggle to vote for Cruz or Trump, but a ton of people would, and before attacking their supporters as sheep or ignorant, be introspective.
Trump says he'll build a wall and the first question that is asked is how. He really has no plan. When people talk about Trump, that's the first thing they bring up. When Sanders says he'll pass things through congress via a political revolution, which more or less amounts to a deus ex machina explanation, people say it's optimism. When he doesn't know how he'll implement his policies in an interview, people come to his defense.
All of these candidates are imperfect. Clinton has a ton of problems, as does every candidate currently in the race. But there are perfectly educated sane people who look at the pros of cons of the candidates available and vote based upon what they think. They may be idealistic, or misinformed, or have a different ideology. But they certainly aren't paid shills. They have simply come to a different conclusion than you have. They may not value optimism, or ideological purity. They may value pragmatism, or have a rosy view of the Clinton era. They may be more ideologically to the center, and they may agree with her more aggressive foreign policy. But man, if votes could be bought and paid shills were a thing, you'd think Jeb Bush would be polling over 0%.
Back to the GMO issue, I was repeatedly accused of being a paid shill. Amusingly, I wish I was. Would have been great to make a few bucks off of Arbcom. God knows we weren't paid for the work we did.