First of all let me say that I've never used or owned any cryptocurrency. I come from the IT field though and I know how they work.
As a lot of people said before me, money in general is a scam. We print papers and agree they have x value. They don't have it inherently.
Once upon a time, a country could print money only if it had gold to back it up. Now that's not true anymore, so goverments (actually the private banks that print money for them) make money appear from thin air.
Even when the gold standard was a thing though, have you ever considered why gold is expensive? Easy one, because it's hard to find. But how we determine the exact price of gold? We don't, we just decide it.
Gold, paper money, bitcoin, oil, stocks, all tradeable assets can be and are manipulated by the big players so that they can profit. Markets are like poker in a way. How much does a pair of eights cost? If you have 10$ worth of chips and 3 people before you raised you are most likely folding. But if you are the chip leader you are definetely playing a pair of 8s, you decide how much they cost and, most likely, profit from them.
All this though doesn't have to do with the actual thing being traded/gambled/manipulated. The fact that the sterling is a scam is not because of the LIBOR scandal for example. Its because, in essence, it's a useless piece of paper with some funny guys printed on it that someone decides that they can make more of just because they can, and we all agreed they are valuable.
In that essence, bitcoin is the least scamy of all money. No one can print bitcoin because he wants too. We need to solve a hard mathematical equation to produce 1 Bitcoin. It's actual labour that produces it, and those who put on the labour take the fraction they helped create. This doesn't happen with any other money, asset, good or service.
Bitcoin trading now, yes, that can be made a scam by some. But that's not inherrent in bitcoin. Bitcoin was not made to be traded like a market asset though. So no, Bitcoin is not a scam.