how I can give them some hints with soft words which can change their mind or at least give them some more space to think twice?
Some people are simply close minded, and there's nothing we can do with that. If I we're you, I'd just explain to them what a "ponzi" really means and how bitcoin isn't a ponzi, because it never promised any returns. Don't waste your time trying to convince people in to an industry that they probably couldn't understand.
Bitcoin is very profitable if we have knowledge on it.Those people that keep on thinking that it is a scam are negative people that was influence by negative sources like social media or fake news on television that has negative information about the existence of cryptocurrency.Most people nowadays will never believe its worth until it is proven but if they were not a part of this community or in this forum by what they hear or read is what they believe.I just think if all people would be resourceful enough to investigate and do some research on it most probably they will come up with doing crypto business like what we already did.