The reason why there has been complains about cryptocurrency generally is just the issue of scam that has made it a popular one, most especially altcoins, he hype of 2017 was great and that is what attracted majority of the people that you see in the cryptocurrency market today.

People expected too much because when they were invited into the market and they came with the mindset of coming to double or triple the investment, but they forgot about the main purpose for which the cryptocurrency itself was established, but because their main expectation was not met, and has been stepped on by the scammers, that is why you see all those noises about cryptocurrency, but bitcoin is still very well respected, and people still love to use bitcoin, you can see from the dominance that it is only altcoins that people are having issue with and not crypto generally.