As a curiosity, a "flash loan" is a loan in which the principal is received and repaid simultaneously and therefore has little practical utility, other than facilitating wash trading and other forms of market manipulation, which are prohibited in regulated markets.
I guess there's those like yourself that would deem it of little practical utility for anyone to borrow permissionlessly and without a large pool a capital of their own to take advantage of arb opportunities that arise in markets (and make those markets more efficient for those that use it). Luckily, defi participants are not bounded by your opinions.
It's unclear whether these flash loans can even be used to exploit arbitrage opportunities. Arbitrage involves simultaneous transactions in different markets, whereas flash loans only allow simultaneous transactions in the same blockchain. Anyway, arbitrage is not a sufficient condition for market efficiency. There's plenty of evidence showing that crypto-markets are rife with fraud and are anything but efficient.
