Its certainly weird to see a crypto leader giving fuel to crypto haters so they can keep on bashing the technology...
I think you're totally mistaken. He has said nothing that can be used for bashing on the technology.
Crypto currencies have countless legitimate usecases - and I don't see "get rich fast" as one of them. His warning is completely legitimate.
Now, if he would have been the leader of BitConnect rather than the chief developer of Ethereum, he would probably have tweeted the exact opposite.
In either case, it doesn't really matter.
Of course his warning is legitimate, but I still don't think making those comments 100% appropriate giving his position. Have you ever see a bankster saying something like "be aware if you have money saved with us, you could lose it all if we fuck up, as we usually do every X years"...
Everyone knows crypto is highly risky, I understand Vitalik wants to be honest, and perhaps the reason he makes this is because he is sure about the long term success of ETH.
Vitalik is not a bankster, and if he had been, I'd probably stay far away from Ethereum.
I believe honesty to be a great virtue; as for myself I would never sell a car without making sure the potential buyer is thoroughly informed about everything that is malfunctioning, even if it means I'll get a lower price for the car.
We do that at work also, we try to be as honest and upfront as possible when responding to questions from the customer, and we do raise flags if we see something that's wrong - even when we earn money on the things that are wrong.
In this case, I do think it's horrendously wrong that people are throwing all their life savings at "cryptos". It is a gamble, particularly if not doing proper due diligence on the coins or tokens one is investing into. Obviously Vitalik is earning money on this in the short term. I think it shows true integrity to warn about this madness.