If crypto becomes unpopular -- so too could Robinhood stock.Robinhood Markets (HOOD 5.72%) stock tumbled 7.1% through 10:35 a.m. ET Monday, and I can explain the reason why to you in three words (and three tickers). They are:Ethereum (ETH 9.37%)Solana (SOL 9.84%)And Bitcoin (BTC 7.47%). On Friday, the People's Bank of China warned of "a resurgence in speculation" in cryptocurrency and "vowing to crack down on illegal activities involving" stablecoins, as Reuters reports. Crypto investors reacted swiftly by ...