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This is one of the flaws of their implementation and many merchants are concern about the volatility of Bitcoin. If El Salvador assess well the situation and try to educate more the merchants or business sector about Bitcoin for sure those things will not happen.
But what still good thing happen is they make Bitcoin acceptance voluntary and merchants could still choose to accept it or not. But if I am the merchant in that country I would provably choose to add Bitcoin since it will not give people choices to pay something for the goods they bought. But also it give exposure to lots of people that my store is accepting Bitcoin. For now the current status is better since they could think about more better approach. BTC still legal in their country so everything still fine and they can deal with Bitcoin on anything they like.
The El Salvador government's policy on bitcoin adoption is considered friendly to economic actors if they do not require everyone to adopt bitcoin as a means of payment. Ultimately this gives freedom to micro or macro economic actors about which is most profitable for their business - but bitcoin seems good to be adopted when the state already supports it.
Accepting bitcoin as a means of payment is a great solution to give buyers multiple payment options. Some people may need to pay in fiat as some places do not accept bitcoin - but this is a decision for each business owner as they are the ones running it after all.