Frankly I think it's obvious that the entire point of quarantines is to hide away the content Reddit doesn't want advertisers to see without any community blowback. Quarantined subreddits are completely ad-free after all.
Was that possible _by accident_ in recent renditions of reddit? IME you have to be in a reddit where that sort of content is, and change settings to make it default visible?
When it comes to visuals, there is a big difference with how comfortable people are with sex vs violence (NSFW/NSFL). Some people would be happy to see one but want to stay away from the other. Then you have the difference within those categories. A picture of a person in skimpy underwear is not the same thing as hardcore porn. Similarly a video of an athlete hyperextending their knee on a sports subreddit is different than the type of gore that you might see on the watchpeopledie subreddit mentioned above.
Maybe you should be able to indicate the severity and category of the NSFW-ness. Potentially something similar to MPAA ratings were you can have PG-13, R, X with an indication if it is for sex, violence, or something else. However that puts even more work on the users/moderators which is probably why Reddit would never implement it.
From the American perspective: our love of and support for free speech means you can make your own website or newspaper and say what you want. (And people have the freedom, conversely, to tell you your content sucks and f you)
But we never envisioned a world where some private newspaper would be forced to print the speech of those they didn't want to, or disagreed with.
Considering the content of the VAST MAJORITY of quarantined subs (holocaust denial, virulent and shocking racism, white nationalism), it's actually shocking that Reddit allows this content to continue without banning.
You say it's sad they are choosing who can speak and who cannot, but I can point you to objectively evil and noxious speech on reddit today that isn't going anywhere...