I've bought things with BTC (I believe I am rare insofar as I have never bought BTC but have spent them...) and having frequently used cash, I can assure you that spending BTC is not even remotely as easy as spending cash.
Digital gold is a better analogy for BTC than digital cash. As a value reserve BTC has a lot of desirable properties over gold (try moving $10m of gold around...). The fact that it's fairly easy to spend BTC is an additional positive point.
Yeah, but ever tried to spend (actual) cash online? Any way you try, you're going to need 2 banks and a payment processor involved. The buyer bank, the seller bank, and Visa, PayPal, or somebody.
In the end, something like 3-5 percent of what you spend is going to be redirected. These are real costs you pay.