While nothing is guaranteed, this is a very shortsighted view and plain ignorant way to look at things.

"doing it themselves"

...Is not an option period.  Traders need speed and liquidity.  And lenders need a intermediary to protect their loan with margin requirements and position liquidations if necessary.

Bitfinex simply provides the platform for doing that.

The reason for such high loan rates right now is because there is high demand and few loans.  As soon as more loans enter the system then the opportunity decreases.  

As with all investments, those who recognize value first get the biggest advantage.

There's no way this opportunity will continue forever.