Spoilers below (albeit for very old, genera classic material)
I'd have to read their exact statements to see if I'm correct, but it might just be that they are using "pornography" in it's proper context as opposed to the way it's been recently used to largely refer to sexual content. The basic idea is that anything that can be considered "offensive and without redeeming value" can be considered pornography. This is a point some people seem to be missing. When I took Criminal Justice many years ago there was a bit on this, as well as how the review process for things in Connecticut worked, where each individual work seeing a complaint needed to be reviewed, and then if it was found to be "pornographic" it would become illegal, as all porn is by definition illegal. Most things people consider porn have never been reviewed due to the simple volume which makes it impossible, and the term is being used improperly in a legal sense since it was never declared to be such. Most "porno" for example is technically "adult art films".
That said to be fair, I'm a huge fan of "Sandman" and enjoyed "Y", that said to be truly understood they need to be taken as entire series to get the context. Taken as individual volumes the way this is being brought up, well, I can sort of see the point. From what I remember of "The Doll's House" it was pretty lurid, even if not the most graphic comic I've ever read, and the subject matter was intended to push the envelope. The context for what was happening and why was largely included for other volumes, as was a proper analysis of Dream's place in the cosmos, and the reasons why he needed to maintain abject neutrality, his inability to do this was part of why he was ultimately preparing for his own "death" and replacement. That said when you get to that serial killer convention, the overall message there is that to each of these people they are heroes in their own mind, and feel justified in what they are doing. Dream winds up threatening to take away their ability to imagine themselves as being good guys. What's more he's there to recover the Corinthian, the ultimate nightmare he himself created, and which was the driving force behind those events. Devoid of greater context it could almost be seen as a sort of tacit approval as long as Dream was not crossed, and after all Dream is respectful of and willing to use his own creation. On certain levels this can be pretty offensive, and while I don't remember it perfectly, any redeeming merits would largely come from context gained from other volumes in the series. The same could likely be said about "Y" because that's a series that is also intending to push the envelope and it's one where the justification and context is spread throughout the entire work, as there are multiple plot twists, and how "wrong" certain things are becomes a substantial part of the entire narrative and the ultimate message which takes a long time to arrive at.
Those making the complaints are wrong, however the teacher probably does need to be spoken to and called to task over their choice of material. Simply using one volume of a lengthy work like this that tells a single, rather complicated, story, is asking for trouble. Rather the class should have focused on one of those series in it's entirely. I could easily see how someone with no familiarity with "The Sandman" could walk away feeling like it was close to endorsing
the worst kind of malevolent behavior. The whole metaphor of dreams needing nightmares, and how when Dream decides he means business he fights with nightmares (and needs what is arguably his strongest one) is ongoing through the series, as well as the specific role The Corinthian is being used for, to protect the new Dream, ultimately he winds up doing things like eating Loki's eyes in a sort of "heroic" role which is intentionally supposed to be at odds with what he did before and what he was created to do. At the level Dream is playing, there are reasons why he needs a nightmare as powerful as a god.
Persepolis strikes me as something that doesn't belong in a fiction class, it's supposed to be autobiographical, and it has a definite very obvious political slant. I wouldn't call it pornographic, but I do think it belongs more in a politics class or something having to do with Middle Eastern studies, to show one particular set of claims regarding the culture. It's not offensive and without redeeming value, unless your even more slanted against Middle Eastern culture than I am by far.
Fun Home is even more of a political piece, and is again autobiographical by the claims of the author, not a work of pure fiction. It belongs in a gay and lesbian studies class or something like that, not in a general class dedicated to fiction. That said to say it's "porn" requires you to be even more slanted than me.
Simply put the first two selections do have some political/social commentary, especially "Y" but both are complete works of fiction and the context is fantastic enough where viewed as a whole and within their own established worlds and logic they aren't even remotely offensive. The latter two are however political pieces that aren't even really fiction which is one of their selling points, and are intended to be non-fantastic in their own way with the intention of selling people on accepting left wing points of view. They are not good fits with the class but hardly offensive.
To be honest, when I first read "offensive graphic novels" for some reason I thought it was going to be stuff by Garth Ennis, and say a class where someone decided to use "Preacher" or "The Boys" both of which are entertaining but I'd honestly have a hard time defending the merits of as anything but offensive entertainment. I mean heck Ennis even mentioned in one interview I read a long time ago that with "Preacher" he hoped nobody would set out to emulate him because it was a carefully calculated and balanced kind of offensive and he figured if someone else did it, it would just be meaness for the sake of meaness. Both of those rapidly undermine any real point they had by intentionally being "okay, so how do I create something even more F@cked up than the last issue". Of course I admit my inner weirdo would love to see a college class being assigned essays on the characterization of "Arseface" and the Russian Super Hero "Love Sausage", or class wide discussion about people who sculpt women out of raw meat in their freezer and have sex with them.... then maybe I could see parents getting offended and wondering what exactly the money they gave their kids for college was being used for. "Hey dad, school gave me a new role model, his name is Billy Butcher...."