Your penultimate sentence contains some sweeping generalizations. Not everyone who submits a review for a class is motivated by spite. Of course, as with any voluntary review system, participation will come from those who are strongly opinionated. But that goes both ways (Also, I could be wrong, but I believe that the site only included numeric reviews...leaving no room for reviews such as “sucks ASS and Booawles!!!!!”, or whatever that means).

Some teachers ARE lousy. And some teachers present the course material in an engaging, captivating manner.

And yes, some students are lazy. But others want to learn, preferably from the latter type of professor. Labeling any student who forms an opinion about a professor as an "entitled [student] who failed after submitting a paper a month late" reveals a lack of faith in the ability of a young adult to take a genuine interest in his educational experience.