Are closed altcoin profits in btc a realized gain? That wouldn't be fair because if I hold them indefinitely they will inevitably be worth 0 and uncle Sam isn't going to reimburse me.
If you trade any of your cryptos for crypto, fiat, or even goods, you're creating a taxable event on which you get a tax break in the case of losses and a tax bill in the case of gains. Doesn't really matter if it's Bitcoin, an altcoins or any other asset.
Apparently there are like-kind exchanges in the US which allow tax deferals, but I'm not at all familiar with how those work. If you could just flip BTCs and alts and defer taxes indefinitely that would be a pretty major thing.
I don't see how moving BTC to another wallet creates a tax event.
The law in the US is a bit fucked up, but basically bitcoin is treated like an equity, such as a stock, for tax purposes.
You don't pay taxes until you sell BTC for fiat currency, or trade it for hard assets, like lambos and mansions.
Moving it to another wallet doesn't, at least not where I live. In the US and in the special case of Coinbase this seems to be a different story though...
Edit: I gave up fixing this posts formatting. The bold is my response.