For me it's more or less cause of fear, I guess. Here in Sweden the ones that gets really REALLY serious sentences in courts are usually the ppl prosecuted for tax evasion and tax related frauds, that kinda stuff. Crime involving violence, robbery, also murder you get away pretty easily.. For example a guy in my town got prosecuted recently for murder, they were able to prove he handled the corpse at some point but were not able to prove that he murdered the guy. So the guy got out and the murderer is still on free foot...fucking bullshit.

Anyhow, I'm not yet paying any tax for Bitcoin cause I've not yet cashed out. But when/if I do I will think more closely about wether or not to pay tax on it. But since the government is spending the tax money on complete bullshit things I'll probably go for the latter.