I think we all accept the truth that products will not be available for purchase in perpetuity. But there's a difference between something going out of print due to lack of popularity and being removed from circulation because some people don't like the contents. And truly we live in a wondrous age! You can actually access most of Marvel and DC's legacy works because they've been digitized and placed online. (I have better access to 1st edition material today than I did in 1994.)
However, we all recognize that some of their legacy content does not reflect the values of DC today. Some older content may reflect ethnic, racial, and gender prejudice that were common in the United States at the time. Those depictions were wrong then as they are wrong today.
No, arguments that rely on reductio ad absurdum cannot be taken seriously. Nobody is demanding or expecting copyright holders to make their products available for purchase in perpetuity.
The same can be argued about DC and Marvel's digital collection. Should we petition those companies to make their products unavailable? How many older movies and television shows?
Are Marvel and DC selling access to their old works? I wasn't aware they had them, I thought most of the old stuff was in the form of digital libraries, and I believe it was Mercurius who stated that Libraries aren't enough (could be wrong) to prevent this from being censorship, because they could be trivially taken down.
And this is where I had to start asking, what then would not be censorship? If a company stops selling a product, is it censorship? You menioned old movies and TV shows, but I know for a fact that there has been a lot of media I have been unable to find in the past. I was trying to find the movie "Tokyo Godfathers" a few years back, and I never could. I heard it was an incredibly moving movie. Was I censored because I couldn't find it?
If no, if "not selling" a product isn't censorship, then we have to move to the next step. The why. Is it suddenly censorship if someone demands the product be taken down? I remember a journalism class I took where we discussed photography and mutliple cases where women demanded that printed ads and articles be discontinued and pulled, because they featured the women, but the women had never consented to be photographed. The one that sticks out was an older woman standing in the window of her home, taken from outside the home. Were they demanding censorship?
What about a biography written about a famous person, including excerpts from their personal journal. A journal the author had purchased from a thief on the internet. If the celebrity demands the book be pulled and not sold with their personal information in it, is that censorship?
What if that biography alleges libelous material towards the famous individual? Is pursuing a Libel case against the author censorship?
And as we drill down, we find that it is only likely to be called censorship when it involves not selling a product, because there were complaints about offensive content towards a group of people, or when presenting true facts and not libel about an individual. But, I also have to wonder if age and notoriety play a role in this. Can I censor Plato's Civilization in any meaningful way? It is a book that has been read, discussed, and allegorically presented for millenia. I might be able to censor it in a small section of the world, but it would be trivially easy for someone to order a copy from somewhere else and have it delivered. And since it has been reprinted by so many publishers, it would be such a monumental task to even attempt to find all the "copies" of it. Or, what if I wanted to censor an obscure song? Something that no one is listening to, no one is playing, and that the majority of people wouldn't even recognize the name of? Can you even censor something like that?
I'm going a little hard into this, but this is the fundamental problem I'm seeing. People are arguing Kwan was calling for censorship, and that this will begin a great tide of censoring all media forever, but realistically, he was asking they stop selling a relatively unknown book. From his perspective, it might have been similar to asking a record seller to stop selling Carl Czerny's third most popular work.
Censorship is a serious issue, it is something which should be taken seriously, but I think people are so sensitive to it, that they are jumping at anything that even resembles it, and taking very extreme positions that I don't know if they've fully thought through the implications of.