<...> Looking at his post history, I would have guessed his first post was here, which was posted on September 21, 2015, 02:20:15 AM <...>

Even if any government tolerated the existence of a second currency (they won't), one that is untraceable would be particularly repulsive to their sensibilities. So, the government can use various justifications (or pass new laws if necessary) that bars businesses from accepting bitcoin as payment. Laws against tax evasion, money laundering, etc. could all apply. Since it is pretty risky to accept even without the government hating it (and represents a piddling amount of actual money), why would any actual merchant accept it?

<...> and his password changed here, approximately a day later.