More like a tax on being ethical or having any morality.
The good point of prediction markets is that they provide information. This information is available to everyone, for free, which benefits everyone.
Insiders help achieve this. Insiders have information and by participating in the market they then expose and share that information. So this is good. If we ban insiders, we're just banning accurate information from getting into the market. If we do that, we might as well just ban prediction markets altogether. I don't have a strong opinion either way on that, but a prediction market without insiders is pointless.
Because they are grossly mis-priced for anyone mildly informed.
Even if you suppose my example is bad, you should be able to envision some case where such hedge is helpful.
The reason it works better is because in a prediction market, the person betting against you has no resources or ability to go after you for fraudulent behavior. Whereas an insurance company has both.
Insurance works on repeatable, predictable risks based on models.
You can't get insurance against a military attack. But you can hedge using a prediction market. It's essentially the version of insurance for one-off events, that relies on wagers since you can't use models.
If people who do the obvious trades (sell oil right now - it's going down) lose money, all you have to do is do the opposite (buy oil right now - it's going down) and gain money. Is it not that simple? You will profit along with the insiders when Trump blockades the strait again, although you won't have such perfect timing.