I think you're misunderstanding the article. It would matter if they were betting against an idea that seems impossible. The point is that they'd have to spend their own credit, and put their own reputation on the line, in order to make the idea seem "impossible." There would be no reason or incentive for people to randomly bet against ideas that seem impossible just because they disliked someone, since it would still cost them; even if they did continue doing so, they would quickly lose all their credit, just like in modern gambling enterprises.

Read this part: "With idea futures, Wegener could have opened a market for people to bet on his theory, perhaps to be judged by some official body of geologists in a century. He could have then offered to bet a token amount at, say, 1-4 odds, in effect saying there was at least at 20% chance his claim would be vindicated. His opponents would have had to either accept this estimate, and its implications about the importance of Wegener's research, or bet enough to drive the market odds down to something a little closer to "impossible". They could not suppress Wegener merely by silence or ridicule.

As Wegener increased his stake, buying more bets to move the price back up, his opponents would hopefully think just a little more carefully before betting even more to move the price back down. Others might find it in their interest to support Wegener; anyone who thought the consensus odds were wrong would expect to make money by betting, and would thereby move the consensus toward what they believe. Everyone would have a clear incentive to be careful and honest!"

Moreover, Hanson doesn't mention that anonymous bets wouldn't be possible; in fact, in the "Killer Peanut Butter" scenario, he brings it up.