It's like saying all computers are basically the same -- which they are -- and then going on to conclude desktops and smartphones and rack-mounted servers are all interchangeable.

Bitcoin may be a great investment asset. Time will tell. But its deflationary nature and its high volatility make it a bad currency. That's in obvious contrast to the original intention, which was a "purely peer-to-peer version of electronic cash would allow online payments to be sent directly from one party to another without going through a financial institution."

See here, for example, for a prominent Bitcoin advocate explaining that he no longer uses it as a currency: http://avc.com/2017/08/store-of-value-vs-payment-system/

This is especially a problem when a currency is used by a lot of people. It discourages economic activity and increases the value of debt. Imagine, for example, that you had taken out a Bitcoin-denominated car loan on Jan 1 2016 with a monthly payment of 1 BTC. That's about $440 at the time, or 15 hours at the median US wage. Now you'd have to work 40x as much to cover the loan payment, or about 20 hours a day just for your car. Meaning you would have been driven into bankruptcy.

Luckily for its users, Bitcoin never really took off as a currency, so their debts are in much more stable national currencies. But as you see with Fred Wilson, many experience sharp regret for the times they did use it as a currency.