Nobody used cryptocurrencies for payment before speculation happened. You had people paying 10k BTC for a pizza and;.. that was it, because they were funny internet coins. The only reason people take cryptocurrencies as payment now is because they have value. Why do they have value ? Because people can speculate on it.
Saying that cryptocurrency should be made illegal is a stupid idea, of course. However, cryptocurrency miners should have to declare their activities and pay much higher electricity prices, so that we could actually use that electricity for more useful things.
EDIT: because the argument of "how is this different than the dollar hurr durr": it's not! The dollar has value because people trust the US government to keep existing, because I can exchange it for actual goods and people want it. The primary goal of the USD isn't to speculate, it's to exchange goods. The same cannot be said about your favorite shitcoin.
The lack of value for funny internet coins doesn't come from it being digital, it comes from being absolutely worthless because noone wants to take it. When a government, a physical entity is formed and says "the US Dollar is the currency we'll use to exchange goods", you have value in the USD because you know you're going to be able to use it. You'll be able to buy your lunch with it, because the state you live in says that you have to take it.
Your bitcoin only has value because it can be used to... have more value. It's worthless, and should speculation be gone, you'll go back to it being an unused toy.
Dollars have value because they force you to pay taxes with them. They used to be valuable to foreign nations, because the oil cartel OPEC used to force them to use U.S. Dollars to buy oil. Nowadays nations can use Dollars, Rubels, and Yuan.
Saying that cryptocurrency should be made illegal is a stupid idea, of course. However, cryptocurrency miners should have to declare their activities and pay much higher electricity prices, so that we could actually use that electricity for more useful things.
EDIT: because the argument of "how is this different than the dollar hurr durr": it's not! The dollar has value because people trust the US government to keep existing, because I can exchange it for actual goods and people want it. The primary goal of the USD isn't to speculate, it's to exchange goods. The same cannot be said about your favorite shitcoin.