Conspiracy theories are self-preserving

I have a hard time responding when friends send me conspiracy theories. 

The conspiracy theories usually have a built-in mechanism for deflecting all criticism.

Friend: "5G is causing covid-19!"

Me: "This has been debunked by reputable scientific organizations X, Y, and Z."

Friend: "Those organizations are all part of the conspiracy!"

Any scientific studies or debunking just get ignored as "part of the conspiracy", so there is no way to disprove them. It is quite frustrating.