Yeah but if your vast majority of users doesn't see it or know where to find it, who cares? I've been a reddit user for 2 years and never encountered the subreddits you are talking about nor have I sought them out.
The "solution" you are talking about is heavy-handed speech moderation
There are three main ways of interacting with Reddit: posting, voting, and commenting. Hiding the obvious hate subreddits helped address the posting of topics. That was an important step and I don't want to diminish it. Reddit has tried to address the voting aspect with various tweaks to the ranking algorithm but whether it has been effective is still debatable. They haven't done anything as far as I'm aware to address hate comments. That is left completely up to the users and moderators.
For the sake of comparison, here is the first paragraph of the Wikipedia entry for each:
Stormfront is a white nationalist, white supremacist and neo-Nazi Internet forum, and the Web's first major racial hate site.
The Southern Poverty Law Center (SPLC) is an American nonprofit legal advocacy organization specializing in civil rights and public interest litigation. Based in Montgomery, Alabama, it is noted for its successful legal cases against white supremacist groups, its classification of hate groups and other extremist organizations, and for promoting tolerance education programs.
I do agree that SPLC and Stormfront do not compare, but it could be argued that Reddit blocks or suppresses conservative, non-multiculturalist views much more than liberal ones. That asymmetry is part of what fuels the growing extremism IMO.
Conservatism goes beyond states rights and economics. It's also cultural. Conservatives tend not to like multiculturalism or cultural change, and tend to like things like gender roles, immigration tests, and just generally keeping things the way they were. Rational and compassionate people can have these opinions too, yet they are suppressed on pretty much all social media sites including Reddit.
When people with moderate cultural views and opinions get suppressed, they cling to the nearest groups with the closest mindset to their own. Unfortunately, on sites like Reddit, these are often extremist subreddits.
/r/The_Donald has broken many rules of Reddit and the largest punishment they've been given is that /r/popular was created to steer people to less toxic content.
You can also look to how long they let /r/physical_removal (advocates of political violence towards "commies" and "leftists") and /r/incels (advocates of sexual assault, rape, and violence against women) stay open.
/r/MensRights is still around despite doxxing and harassing people in the past.
Victims?
It works on HN
when i visit HN, i expect the articles to be topical and for the discourse to be informative and interesting. somewhat amazingly, my expectations are usually met here, which makes the site quite a gem.
at the same time, i don't always want that. sometimes i just want to see a true train wreck unfold in the comments. in a way i even appreciate the donald trump and hate subreddits. if there are ideologies spreading that can impact my life, i would prefer to go to the source and read their actual words than have the ny times regurgitate them to me.
there are benefits to the hands-on moderation and the wild west styles. the only optimal solution is having a wide range of choices.
If those channels become extremist echo chambers, then the government could care when terrorists start being made on the site, affecting Reddit's PR in the long run. I know of several subs that are full of such extremist vitriol. Since they're a global website, they've got to consider things like long-term social impacts of their content.