Why is impact investing slapped with an ‘impact measurement’ tax?

Call yourself an impact investor, and – unlike any other investor – you'll be required to spend time and money proving that you're doing what you say you're doing. Why do we allow impact investing to be uniquely taxed in this way, asks Jesse Clain – with impact consultants "drumming up demand" for their services by claiming that the industry is full of fraud and incompetence?