Holders already expect that bitcoin's price will go down big possibilities and same to Ethereum so many of holders already sell early for their altcoins so they dont loss big enough.
Well, not all holders by the way. A lot of newbies who came into this market late last year did not actually have the mind to hold, but they were forced to hold by their mentality of getting rich overnight based on some promises they decided to give themselves out of greed. There is no danger of holding in the long term as long as you know what you are holding has potential, there is only a huge danger in the short term when you are so much focused at it, and you get all emotional selling at loss, and in that case, such people always end up regretting those actions in the long run.
a lot of people came into this space with some promises of getting rich overnight and they are now stuck in between the deep blue sea (their mind) and the red sea (the market), with confusion and fear all over them.
These are the problems for the people who do not have the plans of holding for years. I am a long term holder and holding bitcoins from the price range of $220 to $300 from the year of 2015 and I am not finding any danger, OP is talking about. Plan for decades and skip all the hassles.