Harm or self harm e.g. go kill yourself, or someone should put a bullet in them, or here’s a guide to how to be anorexic without getting caught.

I think calling someone out on this is more effective than silently banning someone. It's more transparent, and shows that we aren't willing to put up with it. In the case of the last one, probably we would want to remove it and send a DM to them explaining why it's not acceptable. In this case, the harm in leaving it up outweighs the benefit of transparency.

but I also think that a set of defined unacceptable behaviour is not just for determining whom to smite but also for telling new people what kind of place they’ve found.

I'm not sure that we've quite worked out what kind of place this is. But if you have a suggestion that could sum it up in a sentence I'm all ears. However, I don't think we need to say "no threatening, no doxxing, no telling people to go kill themselves" as I think by listing this you are telling people it's a place that needs these common sense rules because people often aren't able to use common sense so need it written down. I'm not sure that's the place we want or the impression we want to give.