Is it really against your consent though? They didn't take the taxes without you knowing. Before any tax is passed or increased the public is notified. So I guess we can take the issue of theft away.

Taxation becomes wrong when it becomes extreme and when the government don't make good use of the taxes. In my opinion, taxes are like payments to the government so they'll be able to continue providing what they're supposed to provide for their citizens. Where it becomes wrong is when you pay your taxes yet don't get anything in return.

Taxing gains from cryptocurrencies is extreme to me too and I agree that it crosses the line. In that case, we can say that they're overstepping. The fact that they're in charge of the citizens of their country doesn't mean the citizens should have no power over themselves. They should have a right to privacy.