This unfortunately happens fairly routinely even at high level universities. Not always as publicly, though, but it does happen.

I'm a faculty brat (professorial parents) at one of the top public universities in the nation. There are always students that will complain to professors that things are too hard, or that grading schemes are unfair, or etc. with very little cause. Possibly worse is that sometimes people's /parents/ will call or email their professor to appeal a grade.

It does seem to be somewhat major dependent: I have /never/ seen it occur in a math class, for instance, whereas it apparently routinely occurs in my mother's English classes. (She's known for grading more stringently than many other English professors. Complaints also don't usually work.) However, I think that it's a mark of an experienced teacher that they don't let bullshit like that faze them: the one time I've seen it really affect how a class was taught, it definitely made the class worse as a learning experience. (Some vocal computer science majors thought that an algorithms course was too difficult, and the professor made it easier, which definitely was a net loss for everyone. I'm very glad that I wasn't enrolled in it.)

I think it's disgusting. Sometimes professors make mistakes: in class structure, or assignment load, or grading something, or the like, and bringing that up politely is appropriate. But if they know they are assigning hard, long assignments, or the grading is fair, or the like, then it's usually for a good reason. The professors who don't care about teaching usually also don't teach hard courses or grade harshly, because it means more work for them.

I agree that generally the people who do things like this are less likely to do well post-college. Either because their parents are hovering over them (see parental phone calls) and they won't ever learn self-discipline and reliance, or because they expect that if they complain, the world will magically bend itself to their will. I think some of it happens when people are taking courses they don't want to take for a requirement, but I agree that there are a good number of people who get sold on the "college degree -> good job and happiness and money."