I don't disagree with this sentiment, but I don't think it is correct to say that Mechanical Turk itself is abusive. Mechanical Turk certainly CAN be abused, but it also CAN be used ethically. For example, we regularly use MT to complete tasks that pay workers effective hourly wages in the range of $8-20 per hour, and I know several other requesters who pay similarly.
It is probably most accurate to say that the lack of worker safeguards on MT attracts many users who pay rates that are (IMHO correctly) classified as abusive. Part of the issue with MT is that traditional worker protections like a minimum wage no longer make sense when you have compensation that is paid on a per-task rather than per-hour basis. Under a per-task compensatory system, faster workers will always earn more money (on an hourly basis) than slower workers. For the tasks we do, it is not uncommon for subsets of workers to earn effective hourly rates almost three times as high as others. In many ways this is good - incenting workers to spend their time on tasks that they can complete most effeciently (and away from tasks that they are less suited for) helps promote the most efficient allocation of labor resources.
But how do you ensure that all workers will always be treated fairly when a minimum wage no longer makes sense? What do you replace it with? Its not clear that there is a simple replacement that works in the micro-tasking context.
Our platform (http://houdiniapp.com) helps businesses complete projects on MTurk. One of the things we realized is that many requesters pay low wages simply because they are really bad at estimating how long tasks actually take to complete. We’ve been able to solve this (somewhat) by providing tools that provide real-time feedback on average completion times in order to provide direct visibility into real hourly wages. However we allow users to set their own compensation and some users still end up paying effective wages in the $2-3 (which we do not encourage, but don't have any simple way to prevent).