This is said not only by Buterin, but also by many other skeptics and analysts.
Think about it, is it worth keeping everything in a crypto? Ask those who hold bitcoins since December 2017 or just bought them in December. Lot of people but it with credits...
You need to understand that there are several strategies here including to hold for a long time or to receive a small profit and fix it by selling crypto. Then buy again. Repeat.
Also you can say about any currency in the world that it can go down and bankrupt.
Think with your head and take consequences of risks that may happen to you.