That imprisonment is given in Bangladesh if found using bitcoins.Some governments fear that bitcoin usage would promote illegal goods trade more and also they would loose their tax revenues.For example,just before two months five youth were caught in india using drugs and their transactions was found to be in bitcoins.So,indian government went to the extent of announcing bitcoin as illegal.But thank god,now it has changed its decision and had shown green flag to legalize bitcoin.Same is the situation with other countries too.
The whole tax revenue story is pretty stupid.
How can you and how will you try to avoid taxation with bitcoins?
You have to issue receipts you have to buy your products from a source you have to pay people.
Even with bitcoin you will still have to do those.
Furthermore it will be even more dangerous to avoid taxation with bitcoin if you're a shop for example.
Getting cash you can toss that in your pants but with bitcoin all the transactions will be there in the blockchain and the details on your computer.
Trust me , tax avoidance won't grow that much with bitcoin.