I sometimes think that news and media overblow the nasty sides of the Internet (the sexist / racist side, the trolls, etc.) way out of proportion. For a taste of what average Redditers are interested in, I perfectly think subscription count is reasonable (more so than activity -- people can be very passionate / post a lot about something that is overall a minority opinion).
I cannot comment on the actual communities themselves other than what I see from a quick skim (I don't use Reddit much), but the top community subjects don't feel very toxic. Jokes, knowledge, games, pictures, cuteness, music. Maybe the big news subs (eg worldnews) get political, for all I know, didn't seem too bad on a quick skim.
None of the top list screams "white supremacy" or "political propaganda" to me (some say "politics", sure, but propaganda?). Due to size, of course, I would expect some moderation is needed for those super-huge communities, but that's expected these days. r/conspiracy (probably the biggest community that steps a little bit into a more paranoid worldview) has a lot of people, but r/science has 30x more.
I would even argue that gonewild (the top "porn" subreddit) is atypical compared to most commercial Internet porn sites, which is probably why it actually cracks the top 100.
Porn and white supremacy constituencies are similar in the context of a VC backed company whose trajectory is tied to an equity event. That is that they drive lots of engagement and probably more time on site.
Reading the article, the author’s point was that pursuit of growth at all costs creates bad situations like echo chambers for racists.
Other sites like Stackoverflow avoiding this sort of situation by being intelligent and strategic about pursuing growth.
Porn offends some people as well (and is not meant to be viewed in certain social scenarios, of course). Reddit has a "safe for work" and "not safe for work" category, and as far as I'm concerned this dividing line is probably better than the no-nudity-period type policies of Facebook (which leads to dramas over non-pornographic nudity, eg breastfeeding photos, a famous Vietnam photo, etc.). It seems like cute pictures and jokes drive more growth to me at first glance then porn, anyways.
Managing "toxic behavior" is a lot trickier, from what I see -- over-heavy moderation also can lead to issues. But "growth at all costs" social media, without checks, leads to factors such as bullying, abuse, and harassment listed as negatives in articles on your growth prospects.
New accounts get subscribed to the defaults automatically -- hence the top ~50 subreddits by sub count are or were defaults.
"User Activity" is probably more accurate. Even then, how are they determining activity? Views? Comments? Up/downvotes?
Regardless of defaults, I doubt there is a single metric that show that porn on reddit is more popular than cat pictures. There is doubt in any method that collect metrics, but if we define them as insignificant then the same metric can not later then be used to say that porn is significant on reddit. Uncertainty cut both ways. Subscriptions can be bots, could be mistakes, might be from users not reading the site, or simply made up. Same goes for view counts or "activity".
Check out this marketing pitch for Reddit ads. https://www.slideshare.net/webjoe/reddit-26009093
Think of the dimensions of use here. I'm sure cat pictures get lots of hits, but I doubt cat pictures drive 20m average visit time.
The biggest porn section in reddit is currently ranked 61 of all subreddits. Cat picture section is ranked 6 and is 18 million subscriptions vs 1.4 for the porn. Do reddit have some 18 times more sinister business relationship with cat shops, veterinarians, and cat food, or should we just conclude that reddit reader are human with human interests and as that goes most people prefer looking at a cat picture while a smaller minority goes to reddit for a dose of nudity.
Go to http://redditlist.com/all and look at what the people want to consume. Celebrate that science is where it is.