There's not much it can be done,you can't persuade them unless they have been given wrong information.If they have legit made research about BTC and still think that it's kind of a joke then it's a hard game to play,you just have to let them change their mind and hope that it does happen.
Yes, unexpectedly those people are trying to change my mind by giving negative aspects of digital systems.
Instead of I am convincing them they are pre-emptively trying into myself. But I'm not that much amateur to listen to them, but I do not have any other go except stopping talking with them.
But I always look for new people to spread awareness on bitcoin ecosystem. I made few people to adopt bitcoin system and they do thank me time to time.