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.