Thing is the lizard-people theory is ridiculous at its face and it could be argued that giving someone like that airtime would harm the lizard-people conspiracy. It's the more mainstream (but still niche) beliefs that are vulnerable in this one-on-one environment, like a debate on man's effect on climate change. There's a pretty general consensus that we are contributing to the change of our planet's climate, but hosting a "both sides" debate on something like this makes it seem like it's an open question. And a motivated bad actor who wanted to shift the needle has many tools at their disposal that an honest person doesn't - lying, misleading, misrepresenting research, or simply pulling the "just asking questions, do your own research!" line.

Sorry to be clear we're both in agreement, I just could see a both-sides-er chiming in that actually a debate on lizard-people would be a bloodbath and therefore everything actually should be presented this way, and wanted to added another issue.

Additionally for another real-world example with more immediate consequences we can look at the whole "vaccines causing autism" issue - something that was completely fabricated by a now-disgraced ex-doctor called Andrew Wakefield, but which gained traction due to being presented to the public as if we just don't know for sure (when we did, and his "research" was utterly eviscerated). Wakefield was basically laughed out of the medical profession, but due to the legwork the media did he's managed to establish himself over in the USA and his work effectively kick-started the modern-day anti-vaxx movement.

That's right and you need some sort of boundary of what are you willing to discuss. Eg. for the guy I mentioned it's very clearly justifying Russian invasion, but then he's open about it.

Of course it sometimes creates other problems. In the end I think root problem is almost complete lack of responsibility for lying to wide public(not even legal responsibility, but just social). As climate change denier you're free to repeat the same disproven BS over and over, without no evidence and nothing happens.