We should keep in mind that all the transactions that are made with the bitcoin are not going through the authorities and that means that they have no way to put a tax on it. I would say that the most important reasn that makes some countries limit the bitcoins use or maybe ban it at all.
Yes government shouldn't apply any tax on bitcoin users because bitcoin is a very helpful way to make our life comfortable in this tough situation which is government cannot handle and that's why poverty is not reduce by government, so bitcoin start this campaign to reduce poverty by this currency and their future will also secure because bitcoin investment will give them a lot of profit, so government should more support bitcoin.