That's a good reply and I can totally see your position.
To me, continued support through the sales of the Mystara PDFs puts it into a middle zone. It's not current in the sense that a setting book has been put out for it in 5e, but it's not exactly relegated to the past, either.
Mystara is also mentioned a few times as a setting in the 5e PHB and 5e DMG. People who want to know more are going to have to look to these past books to find out about the setting and that will lead them to these PDFs.
I certainly don't want to see GAZ 10 banned or "book burned," but I think continued sales should be ended.
Okay, so I guess I will have to explain my theory a little more. There is a distinction between a de jure and a de facto ban. A de jure ban would be, for example, the City of Boston as a matter of law refusing to allow sales of the book, Naked Lunch. A de facto ban would be, for example, people publicly pressuring a company to stop producing a disfavored book.
Now, in both cases it is unlikely to be an actual and total ban. Almost every de jure ban is able to be circumvented- you can just travel outside of Boston in the example I provided. It's the same with a de facto ban- just find a library that already has the product! Heck, technically China isn't censoring or banning anything; it's just private corporations making decisions to not offend the Chinese people with our crazy ideas of democracy and rights for the people in Hong Kong. It's just de facto.
In fact, we often hear these arguments. For example, when certain groups are trying to ban Melissa (formerly George) from yet another library because they don't want their children being exposed to the idea that there are transgender individuals out there, you will often hear them say things similar to, "Well, you can always buy it. Or find it somewhere else. We're not banning it, we just don't want to make it available here."
In today's society, businesses and capitalism are the true driving forces- combine that with the idea of rights-holders in IP, and you can easily see how pressuring rights-holders not to produce (or make available) a work is one of the most effective de facto bans that can exist. Because it's essentially unaccountable- governments and boards might make the wrong decision, but they are accountable to the public and to the law (First Amendment issues). But if you really want to succeed in squelching things you disagree with, you just make the companies make it disappear.
I really think that would be unfortunate. Not because the OP's analysis was wrong (it wasn't). But because I think we should always error on the side of "disclose, and allow people to make their decisions." To remove a book like GAZ10 may not matter much- after all, few people play BECMI, fewer still run it in Mystara, and ever fewer would want that book. But I think that days, months, and years from now there will be people who want to get their own, original copy for all sorts of reasons... even if it is to examine the ways in which early RPGs reflected the casual racism of the culture around them.
IMO, etc. Others might feel differently, but I feel strongly about sunlight being the best disinfectant.