Traditionally, individuals or groups who want to manipulate the market need large amounts of cryptocurrency. But with flash loans, anyone can become a whale in a few seconds. And, as we have seen, you can earn hundreds of thousands of dollars worth of ether in just a few seconds.
DeFi services should not be free, because the platform needs funds to operate, and the network needs gas to execute transactions, but at the same time, these fees should be communicated fairly and transparently. The same is true for token-related fees.