Because bitcoin is entirely decentralized, you need trust no one when using it. When you send a transaction, it is digitally signed, and secure. An unknown miner will verify it, and then the transaction is completed. The merchant need not even know who you are, unless you've arranged to tell them.
That's impossible to see that you will buy to a merchant directly because it requires them to know who you are if
their business is registered. payment system is different from a real currency and there are merchants who accepts bitcoin
but relies on a 3rd party.