If crypto does gain massive adoption and you are able to pay for things in crypto, there would be less of a reason for people to cash out into fiat.
but for this to happen we must have regulations that benefit cryptos, if in the future VISA and Mastercard will accept the bitcoin debit card that work in the world for people to use crypto to make purchases and payments. But what we see now is that Visa, Mastercard and banks look at cryptos as a major obstacle to their business and they do not accept cryptos.
How would government collect taxes from crypto gains then?
many people have answered this question, governments are like flies looking shit, they will always find methods to collect taxes
Also, if something like ETH becomes big, how is the government gonna stop people from making pyramids, ponzis, and scams in general?
there are several ways to reduce scam cases, governments can create laws on how the entire ICO process should follow and the guarantees that these ICOs should give to their investors.