it's only real value is what you assign it or can convince someone else to give you for it.
This is true of all currencies, not just virtual ones.
And it's not like VISA is any less virtual.
VISA is backed by physical currency, even if that currency is only such by fiat, it's still real currency.
Bitcoin will never succeed as the "dream" currency. Its previous anonymity is gone, so much of the cool factor is also missing. All your transactions are subject to governmental scrutiny and now they're being monitored for tax purposes.
VISA is backed by physical currency
It is backed by fiat currency, but AFAIK the lion's share of USD moves around digitally; the physical bills and coins cover only a small proportion of the amount in circulation. Most of it exists as nothing more than numbers on balance sheets.
Sure, until the electricity is gone. Then it's only a fond memory.
If you can't hold it in your hand or physically see it, then the chances are good that it's only real value is what you assign it or can convince someone else to give you for it.
And now that governments are beginning to regulate and tax it, even the cool parts about cryptocurrency are gone.