It has already been mentioned and also the White Hats didn't stop anyone. The hacker got away with $30 million. Initially he used the exploit and moved roughly 28,000 and then almost a day later he had used the exploit to move funds from the 2 other accounts. Also most of these White Hats were probably from Parity trying to limit their fuckup.
That sounds pretty bad for Ethereum. It should make any serious investor wonder what other vulnerabilities are out there that could still be exploited.
I'm not really sure whether or not it's really the problem of ethereum. The parity hack was the problem of parity's multisig codes, not directly related to ethereum blockchain. We'll see POS in ethereum soon, maybe the problems will be fixed more strongly.
In my opinion this is some rumors by some people want the market Ethereum panic in next time after Bitcoin in few months ago, we are know if Bitcoin get issue about SegWit2x in August 1st, most trader will going to FIAT, USDT or some Altcoin have a huge community as Ethereum, Dash ... and this is reason make whales want use the rumors make the price of Ethereum crash in next time