I think if bitcoin users don't pay taxes directly, they will pay it indirectly. More than the government can accept bitcoin completely and impose taxes on users even if bitcoin is decentralized.
Talking about tax involves a very broad discussion. there are two types of taxes, direct taxes and indirect taxes,
That is true as there are certain bills like electricity and water that can be taxed, also consumables or goods can be also has tax like groceries and gas so your paying the tax indirectly. Yes it might affect some the government if people starts to not declare their taxes but remember that they can move the taxes in different things to compensate for the loss.