But I have a gut feeling that there's something bigger at play here and that the American media, which is extremely biased in general towards either the Democrats or the Republicans, might actually be doing a smear campaign against him because he is very much anti-capitalist. Or at least anti-corporation.

The reason it’s always D vs R is systemic. Our election system punishes similar candidates that run against each other. Because of this, our political parties are more like coalitions, made up of a number of different groups who strategically send out only one candidate, which is decided in primary elections.

As a result, the people who end up running third party for president are usually delusional, looking for attention, or intentional spoilers. So the fact that RFK jr has a screw loose is not surprising, and I would be more concerned about a conspiracy if our media elevated him to the level of the other candidates when it is undeserved and detrimental.