You don't need to "try to ban it", you ban it.

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.