Earlier quoted context omitted.
You are wrong. The cryptocurrency industry is also made of real companies hiring real people. For example as of Sep 2015 there were 729 Bitcoin companies employing thousands of people: https://venturescannerinsights.wordpress.com/2015/09/04/the-...
You can't seriously be comparing those the entire rest of the world economy. Cryptocurrency doesn't even register as a drop in the metaphorical bucket.
It makes sense to spend a few hundred megawatts on a system that created thousands of jobs.