Because it's not allowed. But in a free market you would be able to pay with gold and silver.
Well, it depends of the country. I think it will be good to do a search about the legal status of this type of transaction.
Maybe not physical gold and silver, but with redeemable paper notes.
A currency board with gold standard? Unlikely, governments don't want this. And I don't think this would solve the problems with the soreveign currencies. In some countries, commercial banks are creating 97% of the money. A currency board (independently if it's pegged to gold or to another currency) won't stop this.
Because the government forces people to accept them. If the government forced you to accept squirrel snot, that would be useful too. But it doesn't mean it would survive as money in a free market.
Yeah, I agree.
But the point is, when people start accepting other cryptocurrencies, the value of the existing ones will drop.
Cryptocurrencies are an experimental technology. I think those alternative cryptocurrencies are necessary, because innovation is necessary. Also, in a free market, the people have the rights to accept other cryptocurrencies. So, in this case, let the free market do the choices.