I am against a tax on Bitcoins per se - given the principle that Bitcoin was meant to be a currency not an investment asset. I would consider one requirement of this that Bitcoin have fairly stable pricing over the short term (which obviously it does not). As such, given that it is primarily viewed and used as a speculative investment asset, it is appropriate for it to be taxed similarly to other capital gains. As to the particulars, whether it's specifically 30%, the fairness of that IMO is dependent how the tax dollars are spent where you live.