How in the world can you even waste your time on criticising use of a high-tech product that is available only to those with a computer and access to internet? Surely there are those who are exploited much much more than users of MT? Especially, if your own link shows that 82% of survey responders answered that the income was not essential.
This is game theory all over again. If "ethical" people wont use MT, only the bad guys will reap the benefits of the increased efficiency. Shaming people doesn't help much if the "right" option is detrimental to their incentives.
Moreover, your US-centrism is showing in full force. Don't you think that paying an Indian or Romanian 25 cents/hour is disgusting? Ok, you hired some of your friends for $12-15/h for mechanical job. So ethical. Why didn't you do that in an English-speaking part of the world where citizens live for less then $1 per day. Wouldnt it be more ethical?
If you are concerned about education of poor children: spread knowledge about moocs, help with youth coding camps, tutor people or do free seminars.
And if you are really-really concerned about the Mechanical Turk then by all means go ahead and teach people who are on MT how to earn more, that would be so much better than complaining on HN about the ethics of MT.