a law to levy a 10% tax on all fiat-to-crypto conversions and cryptocurrency transfers.
Trading of anything including cryptocurrencies have always been subject to taxation. I've even seen up to 30% tax on trading profit. A lot of countries already have such taxes on cryptocurrency trading so it is not a new thing for "others to follow" after Slovenia does it since they are already behind themselves.
As for "transfers" you can't tax them at all unless they tax the businesses accepting bitcoin payments for each payment which is a different story.
Shouldn't the tax be from crypto to fiat conversion?
If it's fiat to crypto conversion it's almost like taxing unrealized assets like the US proposal of taxing the rich but actually affecting everyone.
Cryptocurrency has value in fiat so if you are holding any of it, It's value in fiat will surely grow and that's the time when you will pay taxes even if you didn't trade it back to fiat. Cryptocurrency tax rate has a range varies from the duration of your holdings. This is the current crypto tax law in US.