I think we ought to let the list and users' votes speak for themselves. In a list curated by users for users with a strict voting system, I think potentially any website is fair game. If the community agrees that 8chan is not place we want to link to, the votes should reflect that. KRyan put it well:
The list is not just a list of random websites; it is a list of our suggestions. Voting indicates (or should indicate) how much we, as a community, recommend a given website...As such, a negative-vote suggestion is one that the community recommends against.
So, given that information, it shouldn't really matter what we link them to, the votes will reflect the community's general attitude to both the site and the answer that contains the site (your suggestion should include reasons why 8chan is good, why it is bad, and especially mention the risks of child pornography). We can always remove largely negative suggestions.
Without the concern for child pornography, I think your question is moot. Whatever we vote here will be largely the same of what's voted on the list. But, there IS the concern there, so lets dive into that. As others have noted, it's not necessarily illegal or against TOS to link to 8chan. Potentially dangerous, but a valid entry. In the interest of fairness and objectivity, we can't in good conscience eliminate a list item if the community thinks it's a valid list item. If the community feels like linking to potential CP is not what it wants to suggest, let the vote reflect that. If you disagree, well......vote! We need not make this more convoluted for the sake of it
So, given that, let's look at the guidelines for a list item
Write answers with an eye to redirecting an off-topic question asker.
The answers should quickly help someone decide where to take their
closed question. Focus on creating a collection of signposts to help
them choose the best site for their current question.
As you've mentioned, complete anonymity has it's risks and rewards, as does the lack of moderation. Sometimes people make long questions that are really just rants or just a means to really explain what this issue is to themselves, and there are several good websites for that behavior, one of which is 8chan.
Avoid answers that focus on suggesting a forum for its own sake, or
just exist because you think it's a good site.
This is a valid complaint against 8chan. We shouldn't list it as an option for the sake of it. Why is it good? why is it bad?
Not all playstyles and personality types are good fits for every one
of these forums; try to indicate the kind of player they cater to
without being hostile/judgemental if that's not your cup of tea.
This is the key, here. If SE isn't the website for this person, we ought to direct them to a potential site that is, or a website that can answer their specific question. 8chan is for sure a website where you can vent your frustrations in whatever language you please, and I'm personally an advocate for letting steam out in the right places.
So, yes, we ought to allow that entry as a valid option.
Whether or not the community thinks so is up to the community.
On a personal note, I don't know what 8chan can offer than 4chan can't, besides a particularly different set of people, and 4chan is closely moderated for illegal activity. As someone that has spent a significant amount of time there since 2009, it has its drawbacks and its benefits. If I want unfiltered opinions, that's a good place to ask an opinionated question. If I want any given question I have to be measured by its attention and not its score (every post bumps, so even a community that largely disagrees with you pushes the question to the top with every post, so you can garner a lot of opinions as long as people are talking, versus a site like reddit, where dissenting opinions can often get lost or deleted), I can post there. If I want broader guidelines of what constitutes an RPG question, I can go there. I would upvote a suggestion for 4chan's /tg/ on certain grounds, but personally not 8chan. That does not change the fact that I think we can suggest 8chan if the community wants to.