Is there a one sentence TLDR in English to summarize?
Mined bitcoins are taxed as earned income.
Step 2: Buy stuff with bitcoins, possibly laundering them.
Step 3: Go to jail for intentional tax fraud. Good luck.
You need to spend those bitcoins to get some use of them - if you do it on a small scale, noone cares about losing 20 cents in tax; if you do it on a large scale, it becomes linked to you. For example - seller reports (for tax purposes) who/where they delivered goods; any bitcoin-money converter links your identity to this income; any bitcoin-vs-stuff barter can be a police sting operation, etc. Denying and laundering income is an old, traditional crime - and the same policing approaches that work with cash laundering will tend to work with bitcoin laundering as well.
Paying taxes costs some amount of money - but saying "good luck with that, tax man" can easily go over to crime/jail category; think twice if you want to go over to that road.
And as I understand it, Finnish people tend to pay their taxes proudly. (Might have something to do with the majority of their workforce being employed in the public sector.)
So I don't think this will really be an issue anyway.
Depending on the specifics, that has the potential to be a massive problem. Let's say you mine $1,000,000 in bitcoins but at tax time, the BTC market crashes and they're now worth $100,000. Do your tax bill now exceed your income?
This isn't a hypothetical scenario - During the .com 1.0 boom, some people cashed in their stock options but kept the stock (to get long-term tax rates on stock that could only go up). A year later, they owed income tax (historical market price - strike price) on stock that was now worthless. (capital losses are limited to $3,000/year but carry forward).
All goods fluctuate in value with time. The fair value from the point of view of taxation is the value when you earned it, whether bitcoin or stock options (maybe with options it's timed at when you exercise, I'm not sure).
Imagine a person who earned $10,000 and chose to buy some stock with it, and then that stock crashed. Did that person get taxed on stock that was worthless? Of course not, they earned money (which was taxed) and chose to invest it in something risky. The person who chooses to keep their stock is no different. They could have chosen to sell, and avoid the risk.
Bitcoin is less liquid than stock, so it is harder for a bitcoin miner to avoid these risks. Nonetheless, that's not the government's fault. Paying tax is a cost of business.
That hardly seems fair. What possible reason could justify that?