If I could unconditionally err on the side of caution, I would.

Unfortunately that isn't how the NSFW toggle is used, and erring on the side of caution any more than necessary comes with drawbacks in terms of post visibility and community growth. It also tilts the userbase of the community more towards users browsing and posting from instances like lemmynsfw.com.

Posts like the this one perform orders of magnitude better when not marked NSFW, which means they reach more people who want to see them when untagged, than didn't want to see them.

Tagging them, in fact partially achieves the opposite.

This is because people scroll past content marked NSFW regardless of what it is, except when they are looking for porn.

So while I haven't stopped using the NSFW tag, I push the needle on it a bit by not marking everything even slightly suggestive as NSFW "just in case" because it literally hides the content from the people who want to see it, leaving just the porn enthusiasts to actually see the post, who then down-vote it because it isn't actually porn.

This post isn't going to register as pornographic to anyone seeing a thumbnail, scrolling by, or looking at it over someone's shoulder. At a glance it's just an anime girl. Hence, to me it warrants being left untagged, unlike images that feature immediate apparent nudity or a focus on arousing anatomy that would be visible even in a thumbnail.