Maybe it's just me, but I look at ALL of the tags for wallpapers in judging it's "SFW" nature. If any of them are NSFW, I would expect the wallpaper is now rated NSFW. Example: Nipslip, Nude, etc. Similarly, if any of the tags are "Sketchy", I have to assume the whole picture is sketchy. It's not an average of the number of red/yellow/green tags.
Movies and TV are similar, it only takes one violent scene or one F-bomb to get a movie rated PG-13 or R. The entire film doesn't have to be full of that sort of content to warrant the parental advisory.
By marking an image with an NSFW tag (like all pornstar have and even the keyword "pornstar" has), it implies that all photos with pornstars in them are automatically NSFW. Even if they are sitting in a sunny field fully dressed. It's almost like pinning a "Scarlet Letter" on them - a form of shaming.
Is there some other functional rationale of having all pornstar actresses names automatically be red?