It would be hard for them to enforce taxes if the user knows what they are doing anyway.
Sure, but its not any easier or harder than tracking if someone is evading taxes while is being paid cash under the table. At some point, you need people to just come up and honestly pay their taxes like a "good citizen".
I just think profit on Bitcoin mining or trading etc should be declared as income like any other source of income. Of course if someone wants to do tax evasion, BTC does make it handy.