Short data on WBT, page-419

"If shorting is legal the law needs to be changed such that unwitting 3rd party owners of shares to be borrowed must be informed for consent. Who in their right mind would want their own shares weaponized against them."

This is a good question - and the simple answer is to essentially make money by lending your shares. Most brokers handle this for you if you nominate to participate in the program, InteractiveBrokers offer this feature. I don't know how much you can make. Not every stock can be shorted so there is likely a criteria that needs to be fulfilled first. Perhaps its by market cap, liquidity, some other technical indicators..

Short positions on spec stocks with binary events on the horizon have inherent and obvious risk, but the same can't easily be said of the big index etfs - which have can have large open short positions on them at any time in order to ride the ups and downs. All the while someone is making money by lending their shares and confident enough in the fact that the market is healthy to own those shares and not be bothered by the volatility. This strategey is often performed in an algorithmic fashion and driven by various (and not necessarily overly complex) indicators, leverages very cheap brokerage agreements, and can be in and out of the market within fractions of a second.

An excellent book (great audio book too) on the topic is Dark Pools: The Rise of A.I. Trading Machines and the Looming Threat to Wall StreetBook by Scott Patterson. Anything about Jesse Livermore is also a great way to understand market making.