Has FN ever asked a lawyer about this issue?

This is Pandora's Box. This content is straight up illegal to even view in a lot of developed countries. It's not a question of censoring distasteful content - it's a question of legal jeopardy to both users of the site and FN.

Is FN liable when its moderators fail to tag something that's problematic? Is FN liable when a moderator views content that is illegal to view in the moderator's jurisdiction as part of that moderator's official duties? Assuming that FN is US-based, what happens when a prosecutor gets interested in something going on here from any of the 50+ separate jurisdictions with overlapping laws (this is why legal grey areas are not safe places to be in the US)?

The fact that a lot of other sites out there ignore these questions and just host this stuff anyway doesn't make it wise to dismiss this stuff, but rather just means those sites are incompetently managed and potentially put their users at risk.

In some jurisdictions, this content is in a grey area, and in others it's likely illegal. The idea that a site would make users take affirmative actions to avoid viewing highly problematic content is not a reasonable stance, and not a reasonable way for a website to treat its users.

It goes further than just the first-order question of legality: regardless of it, most sensible adults do not want to be associated with something that has such a large appearance of impropriety. I count myself among them. For that reason, I'll avoid FurryNetwork and embrace alternatives if the current stance holds. I also don't see FurryNetwork winning out as the go-to alternative to FurAffinity if this is a live question; it's a deal-breaker for a lot of people and more important than the relative quality of the site.