Not my native language lol. I'll try again:

Lets say the capital gains taxation rate is 25%.

Scenario 1: I buy 10kUSD worth of BTC, later spending them getting 12kUSD worth of items. I need to pay 2k * .25 = 500 USD in cap.gains tax.

Scenario 2: I buy 10kUSD worth of BTC, spend them for 8kUSD of items. I have a 2k loss that that lessens my tax burden by 500 USD.

In essence, the government is long the total US BTC holdings multiplied by the effective capital gains taxation rate. BTC goes up, they get more money. BTC goes down, they get less money. It's the same exposure as a long BTC position.

At the same time, since the 20% appreciation/depreciation only shows as 15% in my pocket, the volatility has effectively been dampened by 25% due to the IRS sharing my exposure.

Because of this the government is hugely long BTC, this can't be bad for bitcoin.

Another aspect is that bitcoin is 25% less volatile for US users, perhaps making it more useful as currency.