my point is that bitcoin's value can not ever go to zero because there will always be demand for it from users of black markets on the internet.
they have no choice but to use crypto currencies.
as long as the bitcoin network has the most secure hash rate as well as the most liquidity when converting to fiat they will choose to use bitcoin.
If black market is the only place for crypto coins, then other anonymous coins such as Monero have more usage.
for now it seems they are all using bitcoin.
i guess bitcoin is anonymous enough for their needs and the liquidity in fiat conversions gives bitcoin a big advantage over anything else.