Using MTurk for personal surveys and expecting to get good and meaningful results from it is just all kinds of wrong. I do hope there isn't "serious" research that's being done this way.
This article [1] was linked from a Wired article earlier that touched on the same question. To editorialize, undergraduate students are not considered in it to be a much better sample than properly run MTurkers.
You would be surprised how many serious studies you will find mturk as a data source of you dig into them. It's usually buried and sometimes I think they likely omit that little fact all together.
what evidence do you have to support this attitude?
If I had to guess as to his reasoning, it's because Mech Turk is artificial AI.
You wouldn't survey an AI and expect to get anything meaningful.