You cannot solve contract/legal problems and wrong transactions through decentralization. You can't also make a democratic system act on every conflict. You assign a central authority to act on them and you select that authority through a democratic process, which is what we already have. - I want to have a beer! - ok, scan this QR, and accept the transaction - there you go! - thank you, here are your 5 beers - oh, d…
How is this different from cash?
It's just that in the case of btc, there's no central authority to cancel the transaction. You need a court order to force the bar to manually send the money back to you. The bank cannot freeze the funds. Enforcement is crippled. If this is not a reputable business (unlikely for a bar and very unlikely for a small sum like that but bear with me), it's way more likely to lose your money.
This is one of the reasons why money transactions are hard and costly. You cannot pretend that a blockchain fixes all that.