I guess being able to scan each and every cell for the cancerous mutation is also a possible solution, but also a tall order.
10 years ago I had some friends who were into online sports betting. It required getting a VPN, accessing offshore servers, signing up for sketchy websites, and linking an online bank account. It was enough hoops to jump through that the average person wouldn't bother. Back then I would have agreed with you: let the people play! But I'm only 33 and I've watched online gambling cripple peoples' lives in just the last few years. It's a huge problem and should be made illegal again. You should not be able to access it in one click from the App Store.
You may not be aware of how rapidly and historically unprecedented gambling has spread in the US in the last few years. More than half of all men aged 18-49 participate in some form of online sports betting (https://futurism.com/future-society/men-aged-18-to-49-hooked...)
Prediction markets are a way of effectively placing a "bounty" on something you would like to happen. Or capitalizing on one of these existing bounties because you're able to affect the result. It's a way to commodify power (and information of course, which is what these platforms bill themselves for), converting it into money, which can you can build further power with.
So it's not surprising someone would be against restricting gambling. The hard part is to how the gov should do it. But it's not government's job to please every single person.