You can't prove all of them wrong because there will always be some people who dont belive in bitcoin and will call it a scam, a ponzi scheme or a bubble. That's not happening only with bitcoin, in almost all investment some people belive they are good while some people think they are scams. For example forex, I think it is a profitable investment if you are a specialist in doing this thing but a lot of people think that the odds are not in ypur favour and forex trading is something like gambling wich could be if you are a newbie and invest in everything you find.
It's frustrating to see that there are people who call it a scam, crime or whatever you call it, without learning what bitcoin truly is. It's unfortunate to see that people lack knowledge about bitcoin. Sure, I want to see them that they have the wrong perception about bitcoin but everyone will have different opinions about it anyway.