I wish Aaron Swartz were still here. Such an absolute injustice.
Reddit absolutely had issues in the early days (ie: violentacrez), but the issue was mostly a dogmatic concept of free speech, rather than the moderation, and manipulation now. When your subreddit's user-base in in the hundreds, or thousands, rather than millions, it's much easier to pin down bots, and bad actors.
Even subreddits that don't deal with health conditions are going to skew a certain way over time just as a result of who hangs out there all the time and who is accepted, so the "reality" you see in a subreddit is not necessarily the true reality of the greater population. (Again, this should be obvious, but it's easy to forget this when you start reading a reddit post and thinking, "I don't agree with all these people, but there are many people with this opinion. Should I be thinking more like they do?")
Then, weird things started to happen. Some of the things I would post/comment would only get one upvote, and my posts would frequently get immediately removed by an auto-mod. A year or so later, Reddit updated their UI, and the posts with one upvote had a message from Reddit saying they were intentionally hidden.
I conclude it's most likely a combination of subreddits auto-blocking people who post in certain subs, and in some cases the Reddit spam algorithm going completely off the rails. I think a few of my blocked posts criticized Reddit or another social media platform, but most weren't really that notable.
That's true of any real community in the physical world, too.
I'd go as far as saying that it's impossible to have fully inclusive and 100% objectively fair community that's also interesting, or even a community. It's not how humans operate, it's not what they want from a community, and even trying to enforce this "perfection" would require infinite resources feeding an omnipresent bureaucracy to moderate perfect order and compliance into people.