Nothing is as easy as it sounds. Even the most common thing undergoes a learning process of how it is done not to mention trading which requires someone's knowledge and skills before fully involved in it.
It would be weird for anyone who doesn't know much about trading would view it as a Ponzi scheme no matter how he or she perceives it ''to trade for some time and earn money". That doesn't make anyone calling trading a Ponzi scheme. What I normally hear from people is how risky trading can be and it is not something someone can enter without having the knowledge and skills.
I think trading is not as easy as imagined when speculating on buying at a low price and selling again at a high price looking how many people mindset with trading is easy way to earn much money and profitable. There are most difference between trading and ponzi have guarantee with how much percentage earning every day although at the end will be collapse. Some one or beginner have miss understanding with bitcoin as ponzi when get loss in trading, but if have experienced they will understand not easily with profitable from trading how many people show their profitable every day.
Beginner better can't high speculated with trading profitable exactly many of them said easily to earn profit with trading and $100 capital will be more $10,000 in short time. Its wrong mindset and beginner need get knowledge first before start trading in cryptocurrency and learn side of risk with bitcoin or altcoin investment.