If it were not technically possible or practically achievable to purchase real goods and services directly with bitcoin and instead, if you always needed to convert bitcoin to fiat to then buy your goods and services, bitcoin would almost definitionally be too centralized as a system to credibly remain censorship resistant or to credibly enforce the rules of the system that make it viable as a currency system (notably its fixed supply).
This doesn't get said enough, but I think it's true: if there aren't many merchants willing to accept Bitcoin in direct trade for goods, the Bitcoin project fails. But even saying that, I'm not sure.