Earlier quoted context omitted.
How is it a scam?
Other than a currency, what gives it value? Artworks for example are unique, but that does not inherently make them valuable.
Why is a new Ferrari so expensive? Ferrari could manufacture a lot more cars if they wanted to. They could also charge less, their margins are tremendous. It's an obvious function of supply and demand. The price is so high because people say it's worth paying that. It's that simple. If all of their customers suddenly decided it wasn't worth paying that, Ferrari would either lower their prices or go out of business.
Even bond ratings are often open to significant subjectivism that can swing their value considerably.
If enough people decide that a Bitcoin is worth $100,000, then that is what they will be worth. That is in fact how most things in the world are valued. Bitcoin's scarcity and the fact that in the near future it will become almost impossible to mine new coins, adds to the premise.
The question is: does Bitcoin's low utility value and ease of trading in proportion to its market cap, particularly open it up to dramatic whims of the mob? Yes, which you see in its volatility. That won't change until or unless it finds greater baselining usefulness.