Certainly I think it would be a very slippery slope to say that any given thing has no place here. Personally I don't object to snuff in stories, and have even toyed with having it in my own work on occasion (including in the one I'm working on now). Though in my case it's the fact that the act is committed that is of interest, not the act itself - most of our stories here revolve around one person exercising control over another, and what greater degree of control can you have than quite literally having someone's life in your hands, and taking it? That idea can be a turn-on, at least to me. But detailed descriptions of one person killing another are simply not erotic to me.
There's no difference in principle between banning the depiction of snuff and banning the depiction of a whipping. Both are a crime, both are frowned upon by most of society, most people get at least a bit weirded out by the idea that people find either one sexy.
But there are limits, IMHO. For instance, I think the age 13 limit is a little low; I'd like to see it at least two years higher, if not three. But I can live with 13; if I find a story with a character of that age I just mentally pretend they're older, or I stop reading, but the simple fact that such material is available here doesn't bother me much. I could probably live with 12 or 11. But if this site ever lowered the age to, say, 5 - that would be the last it ever saw of me.
Is that a logical, rationally supportable position? Not really, in my opinion. But it's how I feel anyway, regardless. I suppose that makes me no different in kind to those who won't come here because snuff is allowed, or scat, or spanking, or whatever.
At the end of the day we are here precisely because we're a little kinkier than most, or a little more honest about how kinky we are, maybe? But that doesn't mean we should have an "absolutely anything goes" rule.