2. The reason it is illegal it is beyond obvious: basic economics and game theory explain you how dangerous it is tying real world events with financial incentives.
You'll just push it underground and it will get even worse.
The cat is out of the bag.
What makes you think that driving betting underground (which means far fewer people will participate) would be worse than the status quo?
If your argument is "people are going to bet and influence world events on the dark web", the argument ignores economics.
The whole point is that the wrong financial incentives exist, the dark web does not provide them, it's hard to access and liquidity is small.
E.g. Trump insiders are unlikely to "tor their iran/venezuela predictions in Monero" and try to influence the events at the same time, let alone how complex would such a system be.
"Pushing it underground" discourages the majority of bettors from using it, and that is a good thing.