Of course you can always lie to the IRS and pay less in taxes than you should according to their regulations.
If you do not get caught then all is well - you are a winner!
If you get caught then you lose and you face:
Paying the taxes anyway
Paying interest on all the taxes you did not pay
Paying huge fines
Going to jail for tax evasion
This is true whether you hide income and capital gains using gold, Bitcoin, good old fashioned US dollars or any other means.
the point is that they will never know, it's more easy to hide with bitcoin, especially if you hide your coins in other altcoin, simply impossible for them to trace all that shit
with gold it's far more easy to get caught, everythign about gold or fiat is traceable, cash the same, people think that cash are anonymous, but they are not, to get cash you need an ATM which is traced
everything that run on visa or mastercard is traced
I wouldn't bet that your Bitcoin transactions are quite as hard to trace as you think. As soon as you have done a KYC verification somewhere, your info is in the system. They can track the coins, I mean that is the point of the blockchain!
Once you get into alts they will get you by auditing exchanges.
We are lucky in Germany that if you buy and hold for 1 year, tax isn't an issue. I think tax could be what destroys bitcoin in the future, it is so complicated for businesses.