Linking directly to a site with hate speech should be treated like linking directly to any other obscene content; not a big deal, break the link, remind them not to do that, only if they make it a habit should it be considered actionable.
A broken link to such a site to discuss it isn’t a bad thing. For a hypothetical, let’s say a major news site publishes an op-ed denouncing non-hetero relationships and includes hateful stereotypes and slurs, in what seems like an attempt to normalize such opinion and language in advance of an effort to restrict same-sex marriage rights in the US. That’s worthy of discussion and including a (broken) link to the article in question is very helpful if not essential for the discussion.
But it’s another thing entirely to link to such a discussion and to endorse its content in any way. I’d suggest that doing so should be treated the same as if someone wrote those same slurs and hate directly into a post, and moderated accordingly.