What will happen on BTC if the government will said that all the bitcoin holder have to pay their tax??
Maybe the expansion of BTC community will get low than usual.
Trade profits are already being taxed. Crypto tax already exist. It's part of a needed regulation that could actually help increase adoption contrary to your statement. You can't expect to make profit and not pay taxes.
Every country has the tax system that is unavoidable. Every citizen of the specific country is obligated to pay taxes. The countries would fall apart if this system would fail. At the beginning of the crypto revelation, the taxes were avoidable because the government wasn't instructed, and had a lot to learn about newly values. Today there isn't a man which isn't acquainted with the cryptosystem and its capabilities. There are ways of avoiding the taxes but that is also questionable. Everything that you want to hide is revealed sooner or later. The problem with the tax system is not in the system itself but in the specific countries which have higher tax rates than other. When that will be solved I think that everyone will be satisfied with a little loss they are making on the taxable crypto.