There is not a secret as to Oliver's politics. There is an ideological bent to the show, which viewers can take into consideration when evaluating its content and trusting its message. But it also reports a number of stories that are highly salient and deserving of greater public attention, for example:
* Pharmaceutical companies' marketing of drugs to doctors
* Mandatory minimums in sentencing
* Voter suppression tactics and other constraints on voting rights
* DC voting rights
* The limited resources of public defenders
* The "revolving door" in government regulation with the FCC chairman appointee
* Abstinence-only education
* Paid and unpaid family leave
* Televangelists' seed-faith practices
* Sweat shop labor in the fashion industry
I, for one, have shown the clip on the FCC and interest group capture when teaching on the relationship between bureaucracies and interest groups. It is a crisp and recent example of the relationship between the communications industry and the federal government and the implications for effective and responsible regulation of monopolies (and of course, with a healthy dose of humor thrown into the mix).
The teacher's resignation provoked a marked response from the school community and led to him rescinding his resignation and ultimately reclaiming his position. But the broader point is that provided that instructors do not present the show as being an unbiased source of information (indeed, as with any op-ed, it should be a starting point for more, important investigation and discourse), one should hardly be justifiably fired or otherwise pressured to resign for using its political commentary as an instructive tool.