The question is one of morality. writers tend to self censor because they have decent sensibilities but others are not so controlled in what they publish, and that may be the point. Writers are initially writing to get published, so we have to please the editor. Self publishing has no such boss.
Therefore, Ness’ concerns about self censoring to avoid offence is a necessary hypocrisy, if it is on anything other than personal knowledge sensu Jackie Kay’s point on memoirs at 1:24:30 in this video of the day’s proceedings (I make a cheeky cameo at 1:39) when there is an extent of extreme material already available via the internet and other sources.
The effect of swamping ourselves with undesirable, censorable material is that all we are left with is a personal moderation, one that is informed by biology via the psychology of decency.
This is an evolutionary development of behavioural psychology attuned to the natural threats to our survival that we encounter within our environment (e.g., infection from rotting meat, therefore a detest of cadavers). We are revolted by certain things for good reason, they set off alarms in our psyche, but moderating ourselves purely to avoid offence when the offending material is freely available elsewhere serves no evolutionary purpose (beyond maintaining cohesion in communities, where there are likely stronger forces at play).