I think it's scary that so many sees this as an attack on crypto. I do not think so - I think this is a warning not to go over the board and be reckless. I also find it a bit scary that he should not be allowed to speak his mind. Politicians and corrupt people tend to tell lies or shut up if it's good for their own case or the bottom line, honorable people tend to be honest and upfront even if it's not in their best short-term interest.
I think crypto currencies should be measured by their utility, usability and potential usecases, not by how much it was growing last week. I think it's very unfortunate and unhealthy that people seem to care only about the latter.
We've been seeing a trend now for a while that people are buying crypto currencies on exchanges, holding it there without caring a bit about anything else than their short-term gains. The price grows because people are buying, and people are buying because the price grows. This is a very unhealthy trend. It can unpredictably flip anytime; one whale sells out, market price falls, and sometimes it can cause a cascade of panic selling. This is what he's warning about. It's better to try damping the growth through such warnings than to go through extreme boom-and-burst cycles. Stable market prices is good for crypto as such, and we will never get stable market prices as long as people are recklessly throwing their life savings into crypto, hoping for a quick doubling of their life savings.
Today you're angry with Vitalik because of such a tweet. Such a tweet may indeed dampen the growth in market cap for a while - but for the true believers, crypto currencies was never about explosive growth of gaining market cap, but about revolutionizing finance. Came to think, many folks will probably be extremely upset with Vitalik if the market crashes and they have lost more than they can afford to lose. Some people have families to feed. There was quite many suicides in the post-MtGox-apocalypse. Would such a market crash be the fault of Vitalik? Of course, if the market crash is triggered by some exceptional bug or some exceptionally stupid tweet, then perhaps - but still, Vitalik is doing tech for the sake of tech, he never intended to be standing on the front stage in what possibly could be the biggest bubble since tulip market crash.
Another thing, he's speaking about all crypto, not ethereum specifically. Comparing it with a CEO of some car factory, it's not that he's recommending people alternative cars, it's more like he's warning people that the stock markets as such may be overheated, and recommending not to invest more than one can afford to lose into stocks.
Stock markets are heavily regulated, it for sure has plenty of disadvantages, but the purpose is to protect the investors. The regulations are far from fail-safe, but still - an amateur may pick twenty completely random stocks from a well-regulated stock market and the probability is high that he'll go in plus on such an investment. The same absolutely cannot be said about the crypto markets. Take up all the 1500+ coins and tokens listed on CoinMarketCap and throw some money on 20 completely randomly chosen tokens, and chances are that you'll lose at least half of your money on scams, and most probably the second half will shrink to a really insignificant value in just some few years. Yet, that's what many of the newcomers are doing - many are picking some seemingly underpriced tokens by random hoping that one of them will explode in value.
I do believe crypto currencies, tokens and blockchains may revolutionize the way we invest money - but the markets aren't mature, the time is not ripe yet.
By all means, keep buying cryptos, I'm even gaining from it personally, just be aware the good old saying "don't invest more than you can afford to lose" even applies more in the world of cryptos than stock markets and real estate!