Do you have to pay income/capital gains if you say take USD to buy Euros, then use those Euros to buy football tickets to see Germany vs. France on a Friday night?  No, then why should you have to with bitcoin?

Do you have to pay taxes on those Euros you bought if they just sit in your wallet/purse inactive even if Euro price appreciates vs the dollar?  No, then why should you have to with bit coin?

Now on the flip side, do you pay taxes/capital gains when you buy Euros with USD and when their value vs USD goes up you sell the Euros for more USD than you started with (thus a profit)?  Yes, then you should do the same with bitcoin.... but really the goal in developing bit coin is to improve the first scenario, not this scenario.... this scenario will be happily pulled up by the first scenario.

The likely IMHO most violated tax depending on each persons applicable laws are sales taxes and all their forms.....