I am against professors who bitch that they are underpaid when they make more (and often far more) than the median HHI income for the country, often don't teach in the summer, have job security and flexibility and make the overall profession look bad by treating students like shit and acting like entitled jerks. They are the reason why the public looks down on professors as a whole. There - is that easier to understand? Maybe you are one of my crappy colleagues?
I mean, I'm not a professor and I have no desire to be one (although I do have a PhD), but relative to any other profession that requires that much (or often less) education and competitiveness in terms of landing a job, they make far less. Professors make much less than lawyers, doctors, C-level executives, and often than PhDs in industry (especially in biotechnology and chemistry) or at think tanks (especially in economics), and in turn they are compensated far less in exchange for their extraordinary job security. Sure they make far more than the median wage, but 1.5% of the population has a PhD...how many median wage workers have 9+ years of higher education (often more if you count postdoctoral fellowships)? They also have to bust their ass to get tenure in the first place.
The job security and the flexibility can't be beat, but it's not exactly like most tenured profs don't work over the summer. The summer is usually filled with research, professional conferences, grant writing, and service for the university, even if they don't teach. Plus, even if they "don't treat undergrads well," a lot of hot shot research professors bring in huge amounts of money to the university in the form of overhead from their grants, which basically allows the university to sustain itself (google NIH RO1 indirect costs if you don't know what I'm talking about).
There are certainly some asshole professors, but in any job that is highly competitive you will find assholes. My father is a lawyer, and there are plenty of self-important assholes in his law firm. Just as there are self-important asshole doctors, CEOs, hollywood actors, politicians, etc. I don't think this is unique to professors.