They are absolutely crazy. There is no defending it. It is something that makes stupid people feel smart. There are easy, verifiable experiments that can be done and they refuse to accept the outcome.
I haven't, and you probably haven't, though if you have, I'd love to hear that story. As I said, they're skeptical of authority and need to run the experiment themselves; some will even flip on flat-earthers who run the experiment and change their minds. Only those who perform the experiment and still refuse to accept the outcome are deserving of being left to their own crazed devices. Until then, they're just ignorant and/or weird.
There are of course people like grifters in the community who don't believe their own words, but the believers won't reason themselves out of this position they didn't reason themselves into.