Prediction markets as a news source are politically unbiased and nonpartisan , and this is what the establishment people here don't like.
Let's for a moment say you're right, and prediction markets do have a flaw (that if someone wants to spend a lot of money making an outcome look more/less likely), that's an imperfection vs the many biases in other information sources.
tl;dr prediction markets financially penalise providing misleading information, whereas traditional media profit from misleading information