I would start by saying everyone has his or her own opinion about something. You would agree with me to a saying that says if you are not informed, you are deformed. People who call bitcoin a fraud or scam have no idea or clues how it works so therefore  they are quick at calling and labelling bitcoin a fraud, ponzi and scam. You would agree with me that if you really want to know more about something you go into research a d findings about that thing but the reverse is the case. They are not ready to do so but some may have gotten some experience of fraud that is why they just concluded that it is so and maybe they just did not listen to advice and have fallen victim to scammers. Some really do not. I see no reason arguing with them as you can't argue with a blind man. You can only show a blind man the way by assisting him or her but if they refuse you leave them as it is not by force to help them grow. It is a thing of choice.