When it comes to the fixing of the right tax rates, except in the process of law making that makes room for public opinion, that is when our thoughts really matter but for every tax laws, it is expected that the sponsors of those laws and the law makers that will decide on it, down to the head of government that will assent to your bill before making it as laws, will have to put into consideration of of the tenets of a good tax system and that is "convenience" by putting themselves in the position of the tax payer if he would be willing to pay at the rate they are fixing and not just the projected revenue based on the percentage they have set.

For me, I think the rate should be between 10% and 15% but with conditions in that all cost incidental to the earning such revenue should be allowed to be deducted before levying such rate. For example, it will be unfair for me to be charged on a marginal say $100 (difference between the amount I bought and sold) without allowing me deduct the transaction fees for miners by transferring from my wallet to the exchange sites, the one the exchange sites deducted for trading and the withdrawal fees I paid for getting it back to my wallet.