It is true that bitcoin is not likely to be a scam like other altcoins but there is no guarantee that it could be a major crash as we have seen a major crash in 2017 and later in 2018 when bitcoin dropped from $20000 to $3200. But it didn't last long as Bitcoin once again crossed $68k but crashed again to $15k and the present rate is $24k. this is how Bitcoin sometimes undergoes major corrections.
Basically, most of the people from all around the world are familiar with fiat currency and Stocks market where the dump percentage in price were quite low compared to cryptocurrency so that's why when they observe or face a Bitcoin dump with a percentage of 60% to 80% in price, they taught it's gonna be scam as because in stock there is no such kind of big dump and where ever it happen it indicates of bankruptcy, but in cryptocurrency it's totally opposite, we face a lot of big dump but Bitcoin recover it and make new ATH too,
so that why it's difficult for any person to believe in Bitcoin if he is not familiar with Bitcoin or if he hasn't researched about Bitcoin price history, currently most of the people revert to Bitcoin because of the number of profit which people earn. While still a lot of people call Bitcoin a scam because they are not aware of the potential.
You have a point there, the rate at which Bitcoin could buy to reach an ATH and also sell back dangerously could be very scary and discouraging. But that is to the unprofessional people that just dabble into it and it's a very good reason why you need to understand the market you are dealing with before committing your money. Bitcoin is an asset that anyone dealing with it has to fully understand its season, there are bullish and bearish seasons in it. Not that it won't be falling and buying intermittently like any other market but there are major times of the bullish season and the same goes for the bearish season. From what I noticed, the long-term bearish season of Bitcoin where it might be playing almost dead is more than the bullish season where people will start pumping it due to FOMO just like what we see now. Regardless, this shouldn't cause panic if the person is a true trader/investor, they should rather analyze the coin well to know where to buy and when to liquidate their position properly.
Nonetheless, what I believe that scares people most about Bitcoin is that there is nothing backing it as an asset. The only thing backing Bitcoin now is people's money, nothing valuable as a substitute that people could fall back on in case of unforecastable circumstances. But the real enthusiasts dealing with it do not care mainly because of the blockchain technology of the coin, the decentralization and the privacy issue it's being solved for them.